Scales – Pest

Can be serious pests on all types of woody plants and shrubs. Scales are so unusual looking that many people do not at first recognize them as insects. Adult female scales and many immature forms do not move, are hidden under a disklike or waxy covering, and lack a separate head or other recognizable body parts. Scales have long piercing mouthparts with which they suck juices out of plants. They may occur on twigs, leaves, branches, or fruit. Severe infestations can cause overall decline and even death of plants. Most scales have many natural enemies that often effectively control them.

Woody plants heavily infested with armored scales often look water stressed. Leaves may turn yellow and drop, twigs and limbs on trees may die, and bark may crack and produce gum. Many armored scales attack leaves or fruit as well, leaving blemishes and halos on fruit; the fruit damage is often just aesthetic. Some armored scales can kill plants.

Control

Scales are often well controlled by natural enemies, especially when predator and parasite activities are not disrupted by ants or applications of broad-spectrum insecticides such as carbaryl, malathion, or pyrethroids applied to control other pests. If scale populations, especially armored scale species, become abundant, you should take action. In the case of soft scales, controlling ants may be sufficient to bring about gradual control of scales as natural enemies become more abundant. If not, well-timed sprays of oil applied either during the dormant season or when crawlers are active in spring (or, in the case of black scale, in summer) should provide good control.

Dormant-season applications of specially refined oils, often called narrow-range, supreme, or superior type oils, are effective against most scale pests of deciduous trees and landscape plants, especially San Jose scale, walnut scale, and the lecanium scales, but not against oyster shell or olive scales because susceptible stages of these pests are not present during winter. Avoid oils called dormant oil or dormant oil emulsions, which are more likely to injure plants. Treatments can be made any time during dormancy or, for sycamore scale and oak pit scales, during the delayed dormant period, which is the time after the buds swell but before they open. Be sure that the plants are not water stressed to avoid injury. A good time to apply oils is right after a period of rain or foggy weather.

An application of oil or soap alone is usually adequate. One study (of sycamore scale) found that organophosphates (e.g., malathion) combined with oil were no more effective than a properly timed, thorough application of oil or soap alone.

Avoid using the organophosphates chlorpyrifos (Dursban) and diazinon in landscapes and gardens because of problems from their runoff in urban surface water and contamination of municipal wastewater.

Beetles – Pest

Beatles eat plumeria leaves and flowers at night, usually during the month of May/June.  

May Beetles
Phyllophaga spp., Scarabaeidae, COLEOPTERA

DESCRIPTION

Adult — Many species of May beetles (also known as June beetles) occur in any given area. They are shiny, robust insects, reddish-brown to black in color. Oblong in shape, they reach a length of 20 to 25 mm.

Egg — The eggs are pearly white and oblong. Each one, initially about 2.5 mm long and 1.5 mm wide, becomes slightly larger as the larva inside grows.

Larva — Commonly called white grubs, the larvae are white and C-shaped, with a distinct brown head. Young larvae are about 5 mm long, but attain a length of about 25 mm. Two rows of hairs on the underside of the last abdominal segment distinguish true white grubs from similar grubs.

Pupa — The oval, brownish pupae occur within earthen cases.

BIOLOGY

Distribution — More than 200 species of May beetles occur throughout North America. Therefore, a single species population is seldom found. In North Carolina they are most numerous from the Piedmont to the coast.

Host Plants — Although oaks are the favorite food source, adult May beetles also feed on the foliage of many other trees. Larvae prefer lespedeza, sod and corn, but they too have additional host foods which include lawn grasses and nursery plantings.

Damage — Both larvae and adults are destructive. The adults are defoliators, chewing the leaves of various hardwood trees. The grubs feed on and injure the root systems of grasses and other plants. Heavily infested turf can often be rolled up like a carpet, exposing the white grubs.

Life History — May beetles have a 2 or 3 year life cycle, depending upon the species. They overwinter in the soil as larvae in two distinct sizes and as adults that have never flown. In the spring, the adults emerge from the ground in the evening, feed on tree leaves, and mate during the night. They return to some sheltered site in the morning. Females then enter the ground to deposit about 50 eggs in earthen balls. The egg-laying period lasts a couple of weeks. In 3 to 4 weeks, grubs hatch from the eggs and feed on dead organic matter, later moving to the roots of plants. The larvae molt twice, the second and third instars being the overwintering forms. In late August, the second and third instars burrow over 1 meter deep into the ground to hibernate. The larvae do the most damage during the second year. In early spring, third instar larvae construct earthen cells in which they pupate. Adult beetles emerge from pupal cases in late summer, but do not leave the ground; instead, they overwinter there and emerge the next spring.

CONTROL

Sections of turf approximately 929 sq cm (1 sq ft) and 5 to 10 cm (2 to 4 in) deep should be examined for May beetle grubs. On golf fairways, 10 to 12 samples of this size should be taken. If examination reveals an average of three grubs per 929 sq cm (roughly 1 sq ft), treatment is probably necessary.

For specific chemical control recommendations, consult the state agricultural extension service.

Leaf Miner – Pest

Any insect which lays its eggs in the spongy layer between the upper and lower surfaces of leaves is known as a leaf miner. Larvae develop between the leaf surfaces and tunnel or ‘mine’ out the spongy middle layer as they grow, giving leaves a spotty and brownish appearance. The four stages of its development are: egg, larva (leaf miner), pupa, and adult (a small fly).

Control

Although the mines may be considered to be unsightly, this pest can be tolerated as it has little real impact on the health and vigour of a holly. Leaves with mines may turn yellow and drop in early summer but this is the natural shedding of older leaves and not due to the pest.Pinch the leaves of small trees to kill the leaf miner.Insecticides are unlikely to be effective as the thick glossy surface of holly leaves means that sprays run off the foliage and do not penetrate to where the grubs are feeding. On small specimen plants it is feasible to remove mined leaves but not if this would result in significant defoliation.When the leaves are fully formed in late April or early May, this is your first opportunity to use insecticides. Managing leaf miners at this time can significantly reduce the chance of a problem later in the season. In June, if populations are severe, time your insecticide application to coincide with the second period of adult flight. Once you’ve noticed that the larvae have left the leaf, start to look for adults emerging two to three weeks later. Apply insecticides when most of the adults have emerged. Using insecticides to manage late season generations is generally not worth it. If late season problems are severe, consider an insecticide application next spring.

Nematodes – Pest

Microscopic, eel-like roundworms. The most troublesome species in the garden are those that live and feed within plant roots most of their lives and those that live freely in the soil and feed on plant roots.

Root knot nematodes usually cause distinctive swellings, called galls, on the roots of affected plants. Infestations of these nematodes are fairly easy to recognize by digging up a few plants with symptoms, washing or gently tapping the soil from the roots, and examining the roots for galls. The nematodes feed and develop within the galls, which may grow to as large as 1-inch in diameter on some plants but are usually much smaller. The water- and nutrient-conducting abilities of the roots are damaged by the formation of the galls. Galls may crack or split open, especially on the roots of vegetable plants, allowing the entry of soilborne, disease-causing microorganisms.

Control

Management of nematodes is difficult. The most reliable practices are preventive, including sanitation and choice of plant varieties. Existing infestations can be reduced through fallowing, crop rotation, or soil solarization. However, these methods reduce nematodes primarily in the top foot or so of the soil, so are effective only for about a year. They are suitable primarily for annual plants or to help young woody plants establish. Once an area or crop is infested, try to minimize damage by adjusting planting and harvesting dates and irrigation or by the use of soil amendments.

Nematodes are usually introduced into new areas with infested soil or plants. Prevent nematodes from entering your garden by using only nematode-free plants purchased from reliable nurseries. To prevent the spread of nematodes, avoid moving plants and soil from infested parts of the garden. Do not allow irrigation water from around infested plants to run off, as this spreads nematodes. Nematodes may be present in soil attached to tools and equipment used elsewhere, so clean tools thoroughly before using them in your garden.

Mealybug – Pest

Mealybugs are part of the insect families collectively known as scale insects. They are soft-bodied, without the outer shell associated with insects in the other scale insect families. Instead, mealybugs are usually covered with a white waxy powder

Mealybugs have sucking mouthparts. Feeding weakens and stunts plants, causes leaf distortion, yellowing, and even total leaf loss. In some cases, plants can be killed. Mealybugs also produce large amounts of honeydew (similar to that produced by whiteflies and aphids), which can coat plants and surrounding surfaces with a sticky layer. A black fungus commonly known as “sooty mold” grows on the honeydew. The presence of honeydew and sooty fungus is one way to detect infestations of these insects.

Life Cycle. The citrus mealybug female can produce about 600 eggs, which are produced in cottony structures called ovisacs. Eggs may be produced with or without males. The eggs hatch in less than 10 days into small nymphs called crawlers. The crawlers move about the plants and locate feeding sites. Once the insects settle, there is not much movement. Under favorable conditions, there may be six generations per year. In reality, generations overlap, so all developmental stages will be present.

Control

Many chemical insecticides list mealybugs.

Non-chemical Control:

– Rubbing Alcohol Spray: Mix 1 to 2 cups alcohol per quart of water. Using undiluted alcohol as a spray is very risky for plants. Since alcohol can damage plants always test your spray mix on a few leaves of plants first. If the spray kills the pests and no leaf damage shows within the next 2 or 3 days, go ahead and spray further, using exactly the same ingredients and proportions you tested. If an infestation is well-established, it will be necessary to make a series of applications, at 10 to 14 day intervals, for mealybug control.

– Insecticidal soap spray according to the dilution on the label but substitute alcohol for half of the water required.

– Horticultural Oil and Insecticidal Soap Sprays: Are effective non-chemical controls for mealy bugs and other soft-bodied pests. Oil sprays suffocate the insects and can aid in controlling scale crawlers and eggs, while soap sprays cause the insects cell membranes to rupture effectively causing it to desiccate.

Snails and Slugs – Pest

Snails and slugs

– move by gliding along on a muscular “foot.” This muscle constantly secretes mucus, which later dries to form the silvery “slime trail” that signals the presence of either pest. Slugs and snails are hermaphrodites, so all have the potential to lay eggs. Adult brown garden snails lay about 80 spherical, pearly white eggs at a time into a hole in the topsoil. They may lay eggs up to six times a year. It takes about 2 years for snails to mature. Slugs reach maturity after about 3 to 6 months, depending on species, and lay clear oval to round eggs in batches of 3 to 40 under leaves, in soil cracks, and in other protected areas.

Snails and slugs are most active at night and on cloudy or foggy days. On sunny days they seek hiding places out of the heat and bright light; often the only clues to their presence are their silvery trails and plant damage. In mild-winter areas such as southern coastal locations, young snails and slugs can be active throughout the year.

During cold weather, snails and slugs hibernate in the topsoil. During hot, dry periods or when it is cold, snails seal themselves off with a parchmentlike membrane and often attach themselves to tree trunks, fences, or walls.

Snails and slugs feed on a variety of living plants as well as on decaying plant matter. On plants they chew irregular holes with smooth edges in leaves and flowers and can clip succulent plant parts. They can also chew fruit and young plant bark. Because they prefer succulent foliage or flowers, they are primarily pests of seedlings and herbaceous plants, but they are also serious pests of ripening fruits, such as strawberries, artichokes, and tomatoes, that are close to the ground.

Eliminate and Control

A good snail and slug management program relies on a combination of methods. The first step is to eliminate, to the extent possible, all places where snails or slugs can hide during the day. Boards, stones, debris, weedy areas around tree trunks, leafy branches growing close to the ground, and dense ground covers such as ivy are ideal sheltering spots. There will be shelters that are not possible to eliminate—e.g., low ledges on fences, the undersides of wooden decks, and water meter boxes. Make a regular practice of trapping and removing snails and slugs in these areas. Also, locate vegetable gardens or susceptible plants as far away as possible from these areas. Reducing hiding places allows fewer snails and slugs to survive. The survivors congregate in the remaining shelters, where they can more easily be located and removed. Switching from sprinkler irrigation to drip irrigation will reduce humidity and moist surfaces, making the habitat less favorable for these pests. Choose snail-proof plants for areas where snails and slugs are dense. Copper barriers can be useful for protecting especially susceptible plants. Though baits can be part of a management program for snails and slugs, by themselves they don’t provide adequate control in gardens that contain plenty of shelter, food, and moisture.

Handpicking can be very effective if done thoroughly on a regular basis. Snails and slugs can be trapped under boards or flower pots positioned throughout the garden and landscape. Several types of barriers will keep snails and slugs out of planting beds. The easiest to maintain are those made with copper flashing and screen. Copper barriers are effective because it is thought that the copper reacts with the slime that the snail or slug secretes, causing a flow of electricity. Vertical copper screens can be erected around planting beds. The screen should be 6 inches tall and buried several inches below the soil to prevent slugs from crawling through the soil beneath the barrier. Snails and slugs have many natural enemies, including ground beetles, pathogens, snakes, toads, turtles, and birds, but most are rarely effective enough to provide satisfactory control in the garden.

Snail and slug baits can be effective when used properly in conjunction with a cultural program incorporating the other methods discussed above. However, baits alone will not effectively control snails or slugs. Several types of snail and slug bait products are available. Baits containing the active ingredient metaldehyde are most common. Metaldehyde baits are particularly poisonous to dogs and cats, and the pelleted form is especially attractive to dogs. Metaldehyde snail baits should not be used where children and pets cannot be kept away from them. Some metaldehyde products are formulated with carbaryl, partly to increase the spectrum of pests controlled to include soil and debris-dwelling insects, spiders, and sowbugs. However, carbaryl is toxic to soil-inhabiting beneficials like ground beetles and earthworms and should be avoided if snail and slug management is all that is required. Metaldehyde baits containing 4% metaldehyde are significantly more effective than those products containing only 2% metaldehyde; however, they are also more toxic to dogs and wildlife. Most currently available 4% products are formulated for use in enclosed bait stations to minimize their hazard.

Avoid getting metaldehyde bait on plants, especially vegetables. Baits containing only metaldehyde are most reliable when temperatures are warm or following a rain when snails and slugs are active. Metaldehyde does not kill snails and slugs directly unless they eat a substantial amount; rather, it stimulates their mucous-producing cells to overproduce mucous in an attempt to detoxify the bait. The cells eventually fail and the snail dies. When it is sunny or hot, they die from desiccation. If baiting is followed by cool and wet weather, they may recover if they ingest a sublethal dose. Do not water heavily for at least 3 or 4 days after bait placement; watering will reduce effectiveness and snails may recover from metaldehyde poisoning if high moisture conditions occur. Most metaldehyde baits break down rapidly when exposed to sunlight; however, some paste or bullet formulations (such as Deadline) hold up somewhat longer under conditions of sunlight and moisture.

A recently registered snail and slug bait, iron phosphate (available under many trade names including Sluggo and Escar-Go), has the advantage of being safe for use around domestic animals, children, birds, fish, and other wildlife and is a good choice for a garden IPM program. Ingestion of the iron phosphate bait, even in small amounts, will cause snails and slugs to cease feeding, although it may take several days for the snails to die. Iron phosphate bait can be scattered on lawns or on the soil around any vegetables, ornamentals, or fruit trees to be protected. Iron phosphate baits may be more effective against snails than slugs.

Plumeria – Frangipani Caterpillar

The caterpillars are the larvae of the frangipani moth, also known as Pseudosphinx tetrio. At up to six inches in length, the plumeria caterpillar is an impressive sight. It’s bright coloration warns birds and other predators that it is not a very tasty meal. The caterpillar feeds on the plumeria tree, which produces a poisonous sap. The caterpillar is not harmed by eating the sap and it actually makes itself toxic and foul tasting to predators in the process. After the caterpillar gorges itself, it drops and buries beneath the ground to metamorphosize into a large hawk moth. (photo by Hetty Ford)

They feed primarily on the plumeria tree and plant and occasionally Allamanda and Desert Rose. They do not damage crops or ornamental flowers. As to fears of pets like dogs and cats playing with and biting the caterpillars, the insects’ coloring suggests to predators not to eat them as they may be poisonous, and this is understood. I would not recommend anybody eating them or playing with them because they can give you a little nip occasionally. Their destructive nature is evident when plumeria trees became infested with the caterpillars and as little as one week the tree is striped of it leaves, seedpods and flowers. And at the end of it all, they turn into very large, very unattractive brown moths which invade your house at night.

You have three options to deal with these caterpillars. You can:

  1. Do nothing. After the caterpillars have defoliated them, the plumeria plants will recover and produce new leaves again.
  2. Remove the caterpillars from the plants and destroy them.
  3. Spray the plants with an insecticide. You can use a systemic insecticide such as Perfekthion®. This insecticide penetrates the leaves so that when the caterpillars feed on them they will be killed. If you want to use an organic insecticide, use NewBt® or Dipel Pro®. If spraying the organic insecticides, it was best to do so in the late evening, after 4:30 p.m., because the insects were sensitive to ultraviolet light. The caterpillars die two to three hours after feeding on the treated leaves. 

Insects – Pests

Insects thrive in more environments than any other group of animals. They live in the air, on and in the soil, and in water. Insects and mites are among the oldest and most numerous animals on earth, with an estimated 100,000 different insect species in North America alone. A typical backyard contains 1,000 or more different insect species. Some estimates say there are 10 quintillion (10,000,000,000,000,000,000) individual insects on earth at any given time. That means there are approximately 300 pounds of insects for every human pound. With that many insects, how is it possible for plants and animals to survive? The vast majority of insects are harmless or even beneficial; less than 1% are considered pests.

For example:

 

  • Insects aid in the production of fruits, seeds, and vegetables by pollinating blossoms. Seventy-five percent of the world’s crops (for food, beverages, fiber, medicine, and spices) and up to 30% of the American diet are the direct result of insect pollination, including many fruits (such as apples, blueberries, and raspberries) and vegetables (such as melons, peppers, and squash).
  • Insects improve the soil’s physical condition by burrowing throughout the surface layer. The dead bodies and droppings of insects serve as fertilizer.
  • Insects consume dead plant matter, joining fungi and bacteria in recycling waste in our environment.
  • Insects are valuable scavengers, devouring the bodies of dead animals and burying carcasses and dung (animal waste).
  • Some insects parasitize or prey on harmful insects.
  • Some insects are important as feeders on weed plants and seeds, helping to keep populations low.
  • Insects serve as food sources for birds, fish, mammals, reptiles, and other animals.
  • Some insects produce products humans use, such as honey, wax, silk, and dyes.
  • Many insects such as butterflies and beetles can add beauty to a garden.

This chapter covers insects’ biological structure, insect life cycles, insect classification, non-insect arthropods, strategies for identifying insect problems, symptoms and signs of plant damage caused by insects, the cultural and biological management of insects, and beneficial insects relevant to horticultural plants in North Carolina.

 

Insect Structures

Adult insects have an exoskeleton, three body regions, three pairs of legs, one pair of antennae, and zero to two pairs of wings. Because legs and other appendages vary greatly to suit the insect’s environment, they are often used to classify insects. Immature insects lack wings.

 

Exoskeleton

 

Unlike humans, insects do not have bones or a skeleton but rather a tough outer body wall, called an exoskeleton. The exoskeleton provides support for the internal organs and serves as a barrier to retard water loss. Once it hardens, the exoskeleton restricts growth of the insect and must be molted so that the insect can continue to grow.

 

The exoskeleton is made of a sheet of cells covered by layers of cuticle. The cuticle contains wax that keeps the insect from drying out and determines how permeable the exoskeleton will be to water. Insects’ bodies are separated into segments, and the cuticle of each segment is formed into several hardened plates called sclerites. These plates are joined together by flexible portions that enable the insect to move. The exoskeleton can be covered with hair, scales, spines, or spurs. The adult insect’s body is made of three parts: head, thorax, and abdomen (Figure 4–1), but the division between the thorax and abdomen is not always obvious.

 

Head

 

The main features of the adult insect’s head are the eyes, antennae, and mouthparts.

 

  1. Eyes – There are two types of insect eyes: simple and compound. Simple eyes (called ocelli) have one lens that perceives light intensity but does not produce an image. Compound eyes are usually large and composed of many small lenses; they can detect movement quite well but do not produce a particularly detailed image. The eyes of most insects are sensitive to color, which helps them to both select flowers to pollinate and detect mates. Some insects can also see ultraviolet light. Many insect larvae, such as caterpillars, have only simple eyes (called stemmata), while adults often have both ocelli and compound eyes.
  2. Antennae – Adult insects have one pair of antennae. Antennae, often referred to as horns or “feelers,” are primarily organs of smell but can serve other functions, such as helping insects perceive humidity changes, vibrations, and wind direction and velocity. Segmented antennae vary greatly in form and complexity and are often useful in identifying insects (Figure 4–2).
  3. Mouthparts – While insect mouthparts differ considerably in appearance, the same basic parts are found in all types of insects (Figure 4–3a and Figure 4–3b). Mouthparts can be used to identify insects, the type of insect that caused plant damage, and the type of insecticide that would be effective in managing an insect problem. There are many types of mouthparts, but most insects fall into one of four categories: chewing, piercing-sucking, siphoning, and sponging. There are also intermediate types, including rasping-sucking (thrips) and chewing-lapping (honeybees, wasps, and bumblebees). In some adult insects, the mouthparts are vestigial and the insect does not feed. The mouthparts of immature insects may vary from those of adults. Larval forms of insects that pupate have chewing mouthparts, regardless of the kind possessed by the insect in its adult stage; for example, caterpillars (larval form) generally possess chewing mouthparts while butterflies and moths (adult form) have siphoning mouthparts. However, nymphs (immature forms of insects that morph slightly with each molt, gradually maturing to the adult form) have the same mouthparts as adults.
  4. Chewing mouthparts leave noticeable holes in leaves, wood, or fruit. Beetles (Coleoptera), caterpillars (Lepidoptera), crickets, grasshoppers, and katydids (Orthoptera), termites (Isoptera), and many other insect orders have chewing mouthparts.
  5. Piercing–sucking mouthparts are a straw-like tube that punctures tissue and sucks fluids from the host. Both plant pests and insect predators can have piercing-sucking mouthparts. They are typical of Hemiptera—(true bugs, aphids, scales, mealybugs, etc.) bloodsucking lice, fleas, and mosquitoes. Plant damage caused by piercing-sucking mouthparts includes stunting, yellowing, distorted growth, and honeydew (excrement produced by some sucking insects), which can lead to sooty mold. In addition, insects with piercing-sucking mouthparts can transmit diseases when they feed. Pesticides applied to the surface of the leaf are less likely to kill an insect because insects feed inside the leaf.
  6. Siphoning mouthparts include a long tube adapted to draw nectar from deep-throated flowers. While they also work like straws, they do not penetrate the plant like piercing-sucking mouthparts. Many moths and butterflies have siphoning mouthparts that may be up to several inches long. When not in use, the tubes are coiled under the head.
  7. Sponging mouthparts are found in house flies, flesh flies, and blow flies, which all have mouthparts with a spongy tip (called labellum) to suck up liquids or readily soluble food.

The mouthparts of immature insects may vary from those of adults; for example, caterpillars (larval form) generally possess chewing mouthparts while butterflies and moths (adult form) have siphoning mouthparts. However, nymphs (immature forms of insects that morph slightly with each molt, gradually maturing to the adult form) maintain the same mouthparts.

Thorax

 

The thorax is made up of three segments (prothorax, mesothorax, and metathorax). Each segment has a pair of legs, and the wings are attached to the last two segments, which also have spiracles or circular openings used for breathing.

  1. Wings—Most adult insects have two pairs of wings. Wings are a membranous outgrowth of the body wall and contain no muscles. Movement, direction and folding of the wings is controlled by special muscles and sclerites of the thorax. Wings are supported by reinforcing structures called veins. Venation (the arrangement of veins in wings) is different for each insect species and serves as a useful means for insect identification (Figure 4–4). Wing surfaces may be bare or covered with fine hairs or scales. The names of many insect orders end in ptera, which comes from the Greek word meaning “wings.” Thus, each of these names denotes some feature of the wings. Hemiptera means “half-winged,” Hymenoptera means “membrane-winged,” Diptera means “two-winged,” and Isoptera means “equal wings.” If the order ends in aptera, it means the adult has “no wings.”
  2. Legs—The most important characteristic of an insect is the presence of three pairs of jointed legs. In addition to walking and jumping, insects use their legs for digging, grasping, feeling, swimming, carrying loads, building nests, and cleaning parts of the body. Legs vary greatly in size and form and can help determine classification (Figure 4–5).

Abdomen

 

The abdominal section contains digestive and reproductive organs as well as spiracles. The abdomen may have 11 or 12 segments, but in most cases they are difficult to distinguish. Some insects have a pair of appendages at the tip of the abdomen called cerci , which are used as sensory structures to help insects detect and identify their environments. They may be short, as in grasshoppers, termites, and cockroaches; extremely long, as in mayflies; or curved, as in earwigs.

 

In addition to six legs, caterpillars may have five (occasionally fewer) pairs of false legs (prolegs) that enable them to move. Prolegs are plump, fleshy, and often hooked to allow the caterpillar to hold onto a plant (Figure 4–6). Sawfly larvae (Hymenoptera) have six or more pairs of prolegs that lack hooks. This is an important distinction to note when looking to manage a caterpillar pest as proper identification of the larvae will aid in selecting an appropriate treatment. For example, some pesticides such as Bt (Bacillus thuringiensis) will work only on lepidopteran larvae and will not work on sawflies.

parts of an insect

Figure 4–1. Parts of an insect.

Different insect antennae.

Figure 4–2. Antennae can be used to identify insects.
A. Pulmose
B. Moniliform
C. Clavate
D. Pectinate
E. Filiform
F. Serrate

mouth parts drawn

Figure 4–3a Mouthparts
A. Chewing
B. Sponging
C. Siphoning
D. Piercing Sucking

mouth parts photos

Figure 4–3b Mouthparts
A. Chewing
B. Sponging
C. Siphoning
D. Piercing Sucking

veins on insect wings

Figure 4–4. Wing venation can be used to help identify an insect.

insect leg line drawings

Figure 4–5. Legs can be used to identify insects.

 prolegs

Figure 4–6. The prolegs are fleshy appendages visible on the left side, true legs visible on the thorax (right side) of both larvae. Top: sawfly with 6 pairs of prolegs that lack hooks. Bottom: pink-washed looper

Insect Life Cycle

A better understanding of insect life cycle stages will help guide proper identification. Positive identification can help determine if there is a need for management and if so, the best timing for that management. Knowledge of insect life cycles can help identify:

 

  1. The life stage(s) of an insect that may cause plant damage
  2. The life stage of the insect that is easiest to manage
  3. Cultural choices such as choosing resistant varieties or adjusting planting times to insure plants are not in a susceptible stage when a pest is most active
  4. How local climate and ecological conditions may affect insect life cycles

For example, seeing caterpillars defoliating a passionflower vine may be alarming until those caterpillars are recognized as the larval form of the Gulf Fritillary butterfly (Figure 4–7) . If the caterpillars are treated with insecticide, the beautiful adult stage of this beneficial pollinator would never be enjoyed. Cutworms overwinter as eggs on landscape debris, so their numbers can be significantly reduced by properly disposing of weeds and other landscape waste in the fall. The larval form would be much more difficult to manage in the spring. Cabbage loopers can devour vegetables in their larval form, but securing row covers when the adult moths are flying around will significantly reduce the number of eggs laid. Insects may look different in various stages of their development, and being able to recognize those stages will guide decisions about when management is necessary and the appropriate timing of that management.

 

As many insects go through their life cycles, one distinctive feature is the phenomenon called metamorphosis. The term is a combination of two Greek words:meta meaning “change” and morphe meaning “form.” Metamorphosis is a marked or abrupt change in form or structure. Some primitive orders of insects, such as springtails and silverfish, do not go through true metamorphosis but increase in size while maintaining the same characteristics.

 

“Gradual” (incomplete) and “complete” are descriptions of how many distinct parts there are in the metamorphosis. Insects that undergo gradual, or incomplete, metamorphosis get larger but do not change their appearance dramatically as they mature. The three stages of gradual metamorphosis are egg, nymph, and adult (Figure 4–8). The nymphs (immature insects) have eyes and antennae, resemble the adults and often have similar feeding habits; however, nymphs are smaller and have no wings. They may have wing pads which are developing wings in young nymphs. As nymphs grow into adults, they undergo a series of molts, where old exoskeleton sheds and new exoskeleton forms. This new exoskeleton expands and then hardens. The stage of life between each molt is an instar. The number of instars, and frequency of molts, varies considerably with species and to some extent with food supply, temperature, and moisture. Many insects that go through incomplete metamorphosis undergo dramatic changes. Examples of insects that undergo gradual metamorphosis include earwigs, grasshoppers and their kin, bugs and their kin, cockroaches, and termites.

 

Most insects undergo complete metamorphosis, passing through four distinct stages: egg, larva, pupa, and adult (Figure 4–9). A larva may or may not have legs, antennae, or compound eyes. Sometimes they appear wormlike or are covered with spines or tufts of hair. Larvae may molt several times but generally do not change their form until they reach the pupal stage. During the pupal stage, the insect becomes inactive and does not eat but undergoes a profound change. Some insects spin a cocoon or web, or roll a leaf around their bodies for protection. During pupation many tissues and structures, such as prolegs, are completely broken down and true legs, antennae, wings, and other structures of the adult are formed. The adult has little or no resemblance to the larval stage and may be associated with an entirely different habitat. The adult insect spends its often short adulthood reproducing. Its food is often entirely different from that of the larval stage. Insects that undergo complete metamorphosis include beetles, butterflies, ants, bees, moths, wasps, flies, and fleas.

 

gulf fitillary caterpillars

Figure 4–7. Gulf Fritillary caterpillars can destroy passion flower vines but they will turn into beautiful butterflies.

gradual metamorphosis

Figure 4–8. Gradual metamorphosis- egg, nymph, and adult.

complete metamorphosis

Figure 4–9. Most insects undergo complete metamorphosis from an egg, larvae, pupa, to adult.

Insect Classification

Identification of the thousands of species of insects would be impossible if we did not organize a standard classification system. Like the plant kingdom, the animal kingdom has major divisions known as phyla. Several of the phyla that contain horticultural pests include:

 

  • Arthropoda (insects, spiders, crayfish, millipedes)
  • Nematoda (roundworms, nematodes, trichina)
  • Platyhelminthes (flatworms, flukes, tapeworms)
  • Mollusca (snails, slugs, clams)

More than three-fourths of the animals known to exist belong to the phylum Arthropoda. Arthro means “jointed” and pod means “foot.” Characteristics common to arthropods include paired, jointed appendages; chitinous exoskeleton; segmented bodies; and bilateral symmetry.

The phylum Arthropoda is divided further into different classes. Table 4–1 describes a few of the more important classes and presents some characteristics that are used to distinguish insects from other arthropod classes. For an arthropod to be further classified into the Insecta class, it must have three body segments and three pairs of legs.

 

Table 4–1. Classes of the Phylum Arthropoda
ClassExamplesMajor Body RegionsPairs of Legs
Malacostracacrayfish, sowbugs25
Arachnidaspiders, mites, ticks1 or 24
Symphylasymphylans212
Insectabugs, beetles, butterflies33

Classes are further divided into orders. The more important orders of the class Insecta are listed in Table 4–2. Insect orders are broken down into groups known as families of very closely related insects. Family names end with idae. Aphididae (aphids), Muscidae (houseflies), and Blattidae (cockroaches) are examples of insect families.

 

Table 4–2. Some Orders of the Class lnsecta and Their Characteristics
OrderCommon NameMetamorphosisMouth PartsWings
Coleopterabeetles, weevilscompletechewing2 pairs
Collembolaspringtailsnonechewingnone
Dermapteraearwigsgradualchewing2 pairs
Dipterafliescompletechewing, piercing-sucking or sponging1 pair
Hemipteratrue bugs, aphids, scalesgradualpiercing-sucking2 pairs
Hymenopterabees, wasps, antscompletechewing2 pairs
lsopteratermitesgradualchewing2 pairs
Lepidopterabutterflies, mothscompletechewing or siphoning2 pairs
Neuropteralacewings, antlions, dobsonfliescompletechewing2 pairs
Orthopteracrickets, grasshoppersgradualchewing2 pairs
Siphonapterafleascompletechewing or rasping-suckingnone
Thysanopterathripsgradualrasping-sucking2 pairs
Thysanurasilverfishgradualchewingnone

Families are further divided into genera and species. These are the most specific levels of the classification system. The house fly, Musca domestica, serves here as an example of classification:

 

Phylum ………… Arthropoda

Class ……………..Insecta

Order …………….Diptera

Family ………….Muscidae

Genus …………. Musca

Species ………….domestica

 

Insects often acquire common names; sometimes one species may have several common names. For example, Helicoverpa zea, when found on corn, is called the corn earworm, but when found on tomatoes, it is called the tomato fruitworm. Common names are often used to refer to large groups of insects, such as families or orders. The term “beetle” refers to the entire order Coleoptera, which includes thousands of different species. The term “moth” refers to thousands of species in the order Lepidoptera.

 

When to space …

When a common name includes the type of insect, the name is two words, for example “honey bee.” However, if the common name includes the name of another order (not the one in which the insect is classified), the name is one word—for example, “ladybug” (also called “lady beetle”) because the insect is actually a beetle rather than a true bug.

Insect Orders Important to Gardeners

The ability to classify an insect to the correct order gives access to valuable information such as the type of mouthparts the insect has. Knowing the mouthparts tells us about the insect’s habitat, how it feeds, and its life cycle and gives clues about useful management strategies, including proper timing for best control.

 

COLEOPTERA(from Greek koleos = “sheath” + ptera = “wings”)

 

Coleoptera—beetles, weevils, and soft bodied larvae, called grubs—is the largest order of insects (Figures 4–10 a-b). These insects vary greatly in size, food, and habitat. They can feed on agricultural, horticultural, and weed plants. Some are insect predators, scavengers, parasites, and decomposers. They may also be pests of stored grain products. Coleopterans occupy almost every habitat in which insects are found. Almost 40% of all insects are beetles. Beetles have a pair of hardened opaque outer wings, called elytra, that meet in a straight line down the thorax and abdomen and that cover the folded second pair of flexible, transparent wings used to fly.

 

In some species only the adult or the larval stage damages plants; in other cases, both the adult and the larval stages cause harm. In still other cases, neither the larval nor adult causes harm. Larvae may feed on roots, stems, foliage, buds, seeds, fruit, or woody tissue. Coleopteran larvae can be distinguished from other insect larvae by their hardened, often dark head, chewing mouthparts, and the presence of spiracles along their bodies. Some common examples of coleopterans include Japanese beetles, wireworms, June beetles, rootworms, striped cucumber beetles, plum curculios, pea weevils, Mexican bean beetles, Colorado potato beetles, flea beetles, weevils, and cane borers.

 

Several characteristics are common to most beetles:

  • Adults have a hardened, dense outer skeleton; size and shape vary greatly.
  • Adults have two pairs of wings; the outer pair is hardened or leathery, and the inner pair is membranous and folds under the front wings.
  • Adults and larvae have chewing mouthparts.
  • Adults usually have noticeable antennae, which can be club shaped, serrated, feathery, bead-like or threadlike.
  • Soft-bodied larvae have three pairs of legs on the thorax and no legs on the abdomen. Weevil larvae lack legs on the thorax.
  • All Coleoptera undergo complete metamorphosis.

DERMAPTERA (from Greek derma = “skin” + ptera = “wings”)

 

Dermaptera (Figure 4–11), known as earwigs, are nocturnal insects that hide during the day in leaf litter, mulch, and under bark. They are generally scavengers or predators. They are believed to be good nocturnal feeders of aphids.

 

Earwigs share several common traits:

  • Adults are moderately sized, elongated, flat, brown insects.
  • They have two pairs of wings: front wings that are short and leathery and leave the abdomen exposed and a hind pair that is membranous and folds under the front pair.
  • Adults have movable forceps (cerci) on the abdomen.
  • Their antennae are threadlike.
  • Adults and nymphs have chewing mouthparts.
  • They metamorphose gradually. Nymphs resemble adults, only smaller or lacking true wings. Their forceps are also softer.

DIPTERA (from Greek, di = “two” and ptera = “wings”)

 

This is the order of true flies (Figure 4–12). Most insects have four wings, but dipterans have only two. The size of the adult varies from less than 18-inch to more than 1 inch. They range in color, and most are soft­bodied. Some adults feed on nectar, some are blood feeders, some are parasites of other insects, and many are predators. Although they are less known than bees, flies are important pollinators. Fly larvae occur in a wide variety of habitats, though many live in some sort of aquatic environment. Plant­feeding larvae generally feed within the plant tissue—for example, leaf miners, borers, and gall formers. Many species feed during the larval stage in decaying plant or animal matter.

 

Common traits for the order include the following:

  • Two adult forewings are membranous and clear.
  • Hind wings are small knobs called halteres, which are used for stabilization during flight.
  • Larvae are legless and wormlike (maggots) or can be aquatic forms.
  • Adults lack chewing mouthparts; they are either piercing or sponging. Larval mouthparts are variable, but many (especially maggots) have simple mouth hooks. They can cause plant damage, but most do not.
  • They undergo complete metamorphosis.

HEMIPTERA (from Greek, hemi = “half” and ptera = “wings”)

 

This order includes true bugs and sucking insects in the former order Homoptera. True bugs include stink bugs, plant bugs, squash bugs, boxelder bugs, chinch bugs, damsel bugs, and the predaceous assassin bugs (Figures 4–13 a-g). Insects in the former order Homoptera include scale insects, mealybugs, whiteflies,aphids, cicadas, leafhoppers, planthoppers, treehoppers, spittlebugs, wooly aphids, and psyllids (Figure 4–14 a-k). The former order Homoptera is now included in this group. Both hemipteran nymphs and adults feed on plants by puncturing seeds, stems, foliage, flowers, or fruit and then sucking the sap. Some hemipterans may inject a toxin into the plant, which causes further damage. Injury to plants is characterized by mottled grey spots on foliage, deformed buds or fruit (catfacing), wilting, or death. Some hemipterans may also carry plant diseases. Some Hemiptera, however, are helpful predators of other insects.

 

Common traits among hemipterans include:

  • Adults and nymphs usually resemble one another.

  • Adults and nymphs have piercing-sucking mouthparts that can cause damage to plants.

  • If pests, both adults and nymphs cause damage.

  • They undergo incomplete metamorphosis; the stages are egg, nymph, and adult. They do not go through a pupal stage.

Common traits among true bugs include:

  • Adults usually have two pairs of wings. The first pair are “halfwings” (leathery at the base and nearly transparent at the tip). The second pair is membranous and smaller; at rest, the transparent tips overlap.

  • Many true bugs give off an unpleasant odor when disturbed.

Common traits among the former homopterans include:

  • Many secrete “honeydew”, especially certain scales, aphids and white flies.

HYMENOPTERA (from Greek, hymen = “membrane” and ptera = “wings”)

 

Hymenoptera (Figures 4–15 a-f) includes bees, ants, beneficial predatory and parasitic wasps, sawflies, and horntails. Their egg­laying organ (ovipositor) is well developed; some are modified into stingers for defense. Males, however, cannot sting. In adult form, hymenopterans can often be found around flowers.

 

Common traits include:

  • Most adults have two pairs of membranous wings (hind wings are smaller).
  • Most adults have a pinched waist.
  • Adults have rather soft or only slightly hard bodies.
  • Some species organize into societies.
  • Larvae are grublike or maggotlike. They have either no legs (wasps, bees, ants) or three pairs of legs on their thorax and six pairs of prolegs (without hooks) on their abdomen (some sawfly larvae).
  • Most have chewing mouthparts, although some adults have chewing-lapping mouthparts.
  • They undergo complete metamorphosis.

LEPIDOPTERA (from Greek, lepid = “scale” and ptera = “wings”)

 

Lepidoptera (Figure 4–16 a-c) is composed of butterflies, moths, and skippers. Not all adults feed, but those that do feed on nectar or other liquid food. Adults do not harm plants, but they lay eggs that hatch into plant-eating larvae with chewing mouthparts called caterpillars. Most larvae feed externally on plant materials; others are leaf miners, borers, and gall makers; a few are predators. We classify larvae based on the damage they cause to different plants. Some of the names for lepidopteran larvae include budworms, cutworms, borers (potato tuberworm, peach tree borer, European corn borer), fruitworms (codling moth, oriental fruit moth, pickleworm, tomato pinworm, squash vine borer), webworms (fall webworm, eastern tent caterpillar), leaf miners, leaf rollers, leaf folders, and leaf crumplers. Other insects in the Lepidoptera include loopers, corn earworms, monarch butterflies, cankerworms, redhumped caterpillars, imported cabbageworms, and parsley worms. Many will pupate in silk cocoons; some do not. Injury to plants is characterized by tears, tunnels, and ragged holes in the affected plant part.

 

Common lepidopteran traits include:

  • Adults are soft-bodied, with four well-developed membranous wings covered with small scales.
  • Larvae are wormlike caterpillars, variable in color, and voracious feeders.
  • Larvae generally have three pairs of segmented legs on the thorax and five or fewer pairs of prolegs on the abdomen.
  • The adult’s mouthpart is a coiled, sucking tube.
  • Larvae have chewing mouthparts that cause damage to plants.
  • Lepidopterans undergo complete metamorphosis and have one or more generations per year.

NEUROPTERA (from Greek, neuro = “veined” and ptera= “wings”)

 

Neuroptera (Figure 4–17 a-d) includes lacewings, antlions, mantispids, and dustywings. Many are terrestrial, but some are aquatic. Many of these insects are predators, especially the larval forms. Antlion larvae live in the sand and construct pit falls to trap prey. Lacewing larvae prey on aphids, mites, and scale insects. Adults tend to be predatory as well. If the larval forms are not predatory, adults will sometimes feed on nectar, pollen or honeydew. Some species are available commercially for biological control.

 

Common traits include:

  • Adults have two pairs of membranous wings with an extensive pattern of veins and cross veins.
  • At rest wings are held flat to the body or held up to resemble a tent.
  • Most are weak fliers.
  • Their antennae are long.
  • Larvae have piercing-sucking mouthparts and are predatory. They do not cause damage to plants.
  • They undergo complete metamorphosis.

ORTHOPTERA (from Greek, ortho = “straight” and ptera = “wings”)

 

Examples of insects in Orthoptera (Figures 4–18 a-b) include grasshoppers and katydids. Food and habitat vary, depending on species. Most orthopterans are plant feeders but they can be predators, scavengers, or omnivores.

 

Orthopterans share the following traits:

  • Adults are moderate to large and often have rather hard bodies.
  • Adults have two pairs of wings. The front wings are elongated, narrow, and hardened; hind wings are broad, many-veined, membranous, and usually fold under front wings when at rest. Some wings are small.
  • Enlarged hind legs are common and assist in walking, jumping.
  • Both adults and nymphs of pest species cause damage to plants.
  • Nymphs resemble adults, but they have wing pads or are wingless.
  • They have chewing mouthparts and can damage plants, but some are predators.
  • They metamorphose gradually.

THYSANOPTERA (from Greek, thysano = “fringe” and ptera = “wings”)

 

Thysanoptera (thrips; singular and plural) are thin, tiny insects with four narrow, fringed wings in the adult stage (Figure 4–19). During their life, they change gradually in size and slightly in form. Several generations occur each year if conditions are favorable. They do not fly well but can travel great distances by wind. Some thrips feed on other insects or mites and are beneficial, but many cause damage to commercial crops. Discolored and distorted flowers and buds or gray speckled areas on fruit or foliage characterize injury to plants. Thrips scrape the feeding surface and suck up the plant’s fluids. Thrips can transmit tomato spotted wilt virus.

 

Common traits of thrips include:

  • Adults are small, around 1 mm in length, soft-bodied insects.
  • They are often present on flowers or leaves.
  • They have two pairs of wings that are slender and featherlike with fringed hairs.
  • They have rasping-sucking mouthparts that can cause damage to plants.
  • Thrips metamorphosis is intermediate (between simple and complete).

Japanese beetle

Figure 4-10a. Japanese beetle, order Coleoptera.

S. Siegers  CC BY – 2.0

Bark weevils

Figure 4–10b. Bark weevils (Cossoninae), order Coleoptera. Though many weevils live on plants, there are also those that live under bark and feed on fungus. The most extreme bark weevils (Scolytine and Platypodinae) can be serious tree pests.

Matt Bertone

Earwigs

Figure 4–11. Female earwig guarding and caring for her eggs, order Dermaptera.

Matt Bertone

diptera

Figure 4–12. A blow fly (Calliphora livida), order Diptera.

Matt Bertone

southern green stink bug

Figure 4–13a. Southern green stink bug (Nezara viridula), a true bug in the order Hemiptera.

Matt Bertone

plant bug

Figure 4–13b. Plant bug, a true bug in the order Hemiptera.

Matt Bertone

squash bug

Figure 4–13c. Squash bug, a true bug in the order Hemiptera.

grassrootsgroundswell  CC BY – 2.0

boxelder bug

Figure 4–13d. Boxelder bug, a true bug in the order Hemiptera.

Anita Gould, Flickr  CC BY-NC-SA – 2.0

chinch bug

Figure 4–13e. Chinch bug (Blissus insularis), a true bug in the order Hemiptera.

Matt Bertone

damsel bug

Figure 4-13f. A damsel bug, predatory beneficial insect, a true bug in the order Hemiptera.

Matt Bertone

assassin bug

Figure 4–13g. Predatory assassin bug, a true bug in the order Hemiptera.

S. Siegers  CC BY – 2.0

scale insect

Figure 4–14a. Scale insect, order Hemiptera (formally Homoptera).

Sam Droege, Flikr  CC BY – 2.0

mealybug

Figure 4–14b. Mealybug, order Hemiptera (formally Homoptera).

Eran Finkle, Flickr  CC BY – 2.0

whiteflies

Figure 4–14c. Whiteflies, order Hemiptera (formerly Homoptera). Greenhouse and citrus whiteflies are the pest species in NC. All whiteflies feed in the phloem and excrete honeydew on which sooty molds often grow. Heavily infested plants may die.

NC State Cooperative Extension

aphids

Figure 4–14d. Aphids both adult and nymphs, order Hemiptera (formerly Homoptera).

Matt Bertone

cicadia

Figure 4–14e. Cicada molting, order Hemiptera (formerly Homoptera).

Matt Bertone

leafhopper

Figure 4-14f. Leafhopper (Sibovia occatoria), order Hemiptera (formerly Homoptera).

Matt Bertone

planthopper

Figure 4-14g. Flatid planthopper, order Hemiptera (formerly Homoptera).

Matt Bertone

treehopper

Figure 4-14h. Thorn treehopper (Umbonia crassicornis), order Hemiptera (formerly Homoptera).

Matt Bertone

wooly apihd

Figure 4–14j. Asian wooly hackberry aphid, order Hemiptera (formerly Homoptera).

Matt Bertone

spittlebug

Figure 4–14i. Spittlebug, order Hemiptera (formerly Homoptera). Adult (left), nymph (right) secretes liquid and whips it into foam and stays inside. This is to protect from predators and also extreme temperature fluctuations.

Rob N Beth, Satish Nikam, Fickr  CC BY-NC-SA – 2.0

psyllid

Figure 4–14k. Hop-hornbeam psyllid, order Hemiptera (formerly Homoptera).

Matt Bertone

honeybee

Figure 4–15a. A worker honey bee (Apis mellifera), order Hymenoptera.

USGS Bee Inventory, Sam Droege  CC BY – 2.0

queen carpenter ant

Figure 4–15b. Queen carpenter ant, order Hymenoptera.

Matt Bertone

braconid wasp

Figure 4–15c. A beneficial braconid wasp, order Hymenoptera. Emerged from lumber infested with powder post beetles (Lyctus planicollis).

Matt Bertone

Parasitoid wasp

Figure 4–15d. A parasitoid wasp (Pteromalidae) checking out freshly peeled bark on Pinus taeda, order Hymenoptera.

Matt Bertone

Sawfly larvae

Figure 4–15e. Sawfly larvae, order Hymenoptera.

Matt Bertone

horntail

Figure 4–15f. Female horntail (Tremex columba), order Hymenoptera.

Matt Bertone

orange sulfer butterfly

Figure 4-16a. Orange sulphur butterfly, order Lepidoptera.

John Gerwin

virgina creeper sphinx moth

Figure 4-16b. Virgina creeper sphinx (Darapsa myron), order Lepidoptera.

Lynette, Flickr  CC BY-NC-SA – 2.0

skippers

Figure 4–16c. Sliver spotted hoary edge skipper, order Lepidoptera.

John Gerwin

brown and green lacewing

Figure 4–17a. Brown (above) and green lacewings, order Neuroptera. Lacewing larvae are predators to aphids.

Matt Bertone

ant lion

Figure 4–17b. Ant lion larvae (top) build small dirt cone traps that prey fall into and cannot get out of. The larva will wait at the bottom with its large mouthparts. The adult ant lion is pictured at the bottom, order Neuroptera.

Matt Bertone

Mansipid

Figure 4–17c. Mantispid, order Neuroptera.

Ken-ichi Ueda  CC BY – 2.0

dustywing

Figure 4–17d. Dustywing, order Neuroptera.

Matt Bertone

grasshopper

Figure 4–18a. Eastern lubber grasshopper (Romalea microptera), order Orthoptera.

Matt Bertone

katydid

Figure 4-18b. Female Katydid (Conocephalus), order Orthoptera.

Matt Bertone

thrips

Figure 4–19. Thrips, order Thysanoptera.

Matt Bertone

 

Common Non-Insect Arthropod Pests of Plants or People in the Garden

 

SPIDER MITES

 

Spider mites are tiny, soft-bodied animals with two body regions, a thick thorax, three (on larvae) or four (on nymphs and adults) pairs of legs, and no antennae (Figure 4–20). Nymphs and adults have sucking mouthparts. They are so small that they are often not discovered until after they have damaged the plant. Foliage, buds, stems, and fruit of infected plants may become red, bronze, rust, yellow, white, or brown from feeding damage. Spider mites spin light, delicate webs over buds and between leaves where they feed. Mite populations are favored by hot, dry conditions and can spread from field or road margins by wind currents.

 

There are several common species:

 

  • Two-spotted spider mites, and near relatives, can be clear, green, orange, or reddish. They have two small spots on the back that are difficult to see without a magnifying glass.
  • Southern red mites are dark red.
  • Clover mites are larger, brown or gray, flat, and have very long front legs.

Some mites are beneficial predators that eat other mites. They generally move faster than the damaging mites and are often less hairy.

 

SPIDERS

 

Spiders have two body regions clearly distinct from one another, separated by a thin waist. Most spiders are beneficial predators. North Carolina has two dangerous spiders: the black widow and the brown recluse. The black widow spider is shy, likes dark places, and spins a characteristically messy web. The female is normally a shiny, black, moderate-sized spider with a red or orange hourglass marking on the underside of the abdomen (Figure 4–21). Males and immature females can have stripes of red, yellow, and black on the abdomen.

 

Brown recluse spiders are only found natively in the far western tip of the state; they are extremely rare in most of North Carolina. Wolf spiders and other hunting spiders are often confused with brown recluses. Brown recluses have six eyes arranged in pairs and a dark brown fiddle- or violin-shaped mark on its head. The spider is light brown or gray with long, delicate legs and is about the size of a quarter when mature (Figure 4–22).

 

TICKS

 

Ticks are parasitic blood feeders of animals and humans. Larvae have six legs; nymphs and adults have eight legs but no antennae (Figure 4–23). Many can carry diseases. Hard ticks have a hard dorsal plate called a scutum and mouthparts that are visible from above. Soft ticks lack a scutum, are soft-bodied, and have mouthparts visible from below.

 

MILLIPEDES

 

Millipedes are slender, somewhat wormlike animals, with two pairs of legs on most of their body segments (Figure 4–24). Very young millipedes have only six legs. But as they grow, they gain more pairs of legs with each molt. This is why millipedes have garnered the nickname “thousand leggers.” Millipedes lay their eggs in damp places. They usually eat decaying plant matter but sometimes feed on the roots of ornamental plants to obtain moisture when the weather gets dry. Ordinarily, more complaints about millipedes occur during wet weather (millipedes like dampness but not long rainy periods), when they may invade people’s homes. When disturbed, some millipedes curl up and secrete a foul-smelling fluid containing cyanide compounds.

 

CENTIPEDES

 

Centipedes strongly resemble millipedes, except that they have longer antennae, a flat cross section, and only one pair of legs on each body segment (Figure 4–25). They are beneficial predators of other arthropods, and they do no damage to plants.

 

PILLBUGS AND SOWBUGS

 

These pests are similar to millipedes in biology and in the damage they cause to ornamental crops, but they differ in that they have only one pair of legs per body segment, for a total of seven pairs (Figure 4–26). Pillbugs can roll up into small spheres; sowbugs usually cannot roll up. Pillbugs and sowbugs are crustaceans (akin to crayfish) and typically live in damp areas under stones, boards, and dead leaves. Pillbugs and sowbugs sometimes crawl into the drainage holes of houseplant pots to feed on decaying organic matter. These pests work the potting mix out of these holes as they crawl in and out at night. In dry weather, they sometimes feed on tender plants, fruits, or roots to obtain moisture.

spider mites

Figure 4–20. Spider mites.

Matt Bertone

black widow

Figure 4–21. Black widow spider (Latrodectus mactans).

Matt Bertone

brown recluse

Figure 4–22. A female brown recluse spider (Loxosceles reclusa). Note the fiddle-shaped marking on the cephalothorax.

Matt Bertone

lone star tick

Figure 4–23. Female lone star tick (Amblyomma americanum) seeks out vertebrates to suck their blood.

Matt Bertone

millipede

Figure 4–24. Millipede (Polydesmida) has two pairs of legs for every body segment.

Matt Bertone

Stone centipede

Figure 4–25. A stone centipede. Centipedes are beneficial insects that have only one pair of legs per body segment.

Matt Bertone

sow bugs

Figure 4–26. Sow bugs (Oniscidea) have one pair of legs per body segment for a total of seven pairs of legs. They are similar to pill bugs but cannot roll up when touched.

Matt Bertone

 

Identifying Insect Problems

 

A detailed picture or an actual specimen is generally necessary for proper insect identification. Photographs can be helpful if they include critical elements. Ensure the subject is in focus as well as large enough to see important features such as legs and mouthparts. Include a scale item such as a finger or a coin in the same focal plane as the subject. Taking several photographs from different angles is helpful.

 

Avoid answering identification questions over the telephone. Describing what an insect looks like over the telephone can be challenging. Ask as many questions as possible to help identify the problem. For example, ask the following: What was the insect feeding on? How many were there? How were they distributed? Does it appear to be mobile or stationary? Does the insect have wings? Try to get as many facts from the client and consult resources before making any decisions on whether the situation warrants intervention. If a specific pest is suspected, advise the client to look online at pictures. Pesticide recommendations are in the North Carolina Agricultural Chemicals Manual. If a specific pest is suspected, advise the client to look online at pictures. When in doubt, ask an Extension agent to help positively identify the insect. If the Extension agent is unsure, a sample may need to go to the Plant Disease and Insect Clinic at NC State University.

 

Indices

 

Pests can be indexed by name and by host plant in pest publications. Cynthia Westcott’s The Gardener’s Bug Book has one of the more complete pest indices by host plant. IPM for Shrubs in Southeastern U.S. Nursery Production: Vol. I also lists insect pests by shrub, shows timing of incidence, and offers management strategies. If the host plant is known, indices can be used to narrow down the list of possible pests. Asking more questions about the size, shape, damage, and secretions of a pest, can further limit the list of potential culprits.

 

Keys

 

Entomologists have designed keys to identify insects. A key is a step-by-step process of elimination using morphological characteristics—such as mouthparts, leg parts, or wing veins—that narrow the choices until an identification is determined. Use of these keys depends on knowledge of basic insect structure. Extension publications The Master Gardener Insect Guide for Ornamentals and Turf (AG-433), Insects and Related Pests of Shrubs (AG-189), and Insects and Other Pests Associated with Turf (AG-268) contain introductory keys to pest identification on the family level. By keying a pest to a family and using the indices of pests by host plant, a pest can usually be identified correctly.

 

Pest Calendars

 

Many pests occur on plants only at certain times of the year. Pest calendars provide approximate dates when certain insects attack plants and in what stage of life the insects will be. Armed with this information, the field of potential pests can be narrowed. For example, a pest is discovered in a lawn in July. It appears to be an immature insect. According to the Turfgrass Pest Management Manual (AG-348), white grubs are usually not a problem in July, so those can be eliminated as a possibility. Refer to NC State’s Ornamental and Turf Pest Calendars for more information.

 

Symptoms and Signs of Plant Damage Caused by Insects

 

Symptoms are descriptions of how the plant reacts to insect damage, whereas signs are the actual evidence that insects leave behind—including frass, feeding traces, castings, dead bodies, and nests. All of this information is used to identify whether the damage was done by insects and if so, what kind of insect.

 

Feeding Habits: The location of insect feeding damage and the types of damage (tissue bitten and chewed versus tissue pierced and sucked) are valuable information in identifying the responsible insect. Types of damage and examples of insects that could be responsible are listed below.

 

  • Chewing Damage
    • Entire leaf consumed (with the possible exception of tough midvein): caterpillars like cankerworms, and webworms (Figure 4–27).
    • Distinct sections of leaf missing. Notches cut from leaf margin (black vine weevil adult); circular holes cut from margin of leaf (leaf cutter bees); small randomly scattered holes in leaf (beetles, chafers, weevils, grasshoppers) (Figure 4–28).
    • Leaf skeletonized: slugs, beetles, pear slug (pear sawfly larvae) (Figure 4–29 a), elm leaf beetle (Figure 4–29 b).
    • Leaf rolled into tube or tied together with silken threads: leafrollers and leaftiers (caterpillars from moths).
    • Tunnels between the upper and lower leaf surfaces. Insect or frass visible when leaf is held up to the light: leaf miners (Figure 4–30).
    • Leaf falls in early summer. Slicing petiole lengthwise reveals insect larva: leaf stalk borers, larva of small moth or sawfly, maple petiole borer.
    • Girdled twigs: vine weevil and twig girdling beetle.
    • General decline of the entire plant or a specific branch. Holes in the bark, accumulation of frass, sawdust or pitch: borers, bark beetles, pitch moths.
    • General decline of plant, chewed areas of roots: root feeders—larval stages of weevils, beetles, and moths, including sod webworm, Japanese beetle, root weevil.
  • Sucking Damage
    • Spotting or stippling on leaf resulting from localized destruction of chlorophyll: aphids, leafhoppers, lygus bugs, thrips (Figure 4–31).
    • Random stipple pattern on leaf: leafhoppers, mites (Figure 4–32).
    • General/uniform stippling, flecking, bronzing or chlorotic pattern on leaf: adelgids, lace bugs on azalea, some thrips (Figure 4–33).
    • Leaf curling or puckering: severe aphid infestations, thrips (Figure 4–34)
    • Reduced growth and chlorosis: psyllid yellows on potatoes and tomatoes, scale, mealy bugs
    • Leaf and stem distortion associated with off-color foliage: aphids (distortion often confused with growth regulator injury)
    • General decline of entire plant or section of a plant as indicated by poor color, reduced growth, dieback: scales, mealy bugs, other root, stem, and branch feeders.
    • In addition to direct mechanical damage, some piercing-sucking insects cause additional damage when feeding by injecting toxic substances or diseases. This can cause a range of symptoms.
  • Other Damage
    • Galls, swellings on leaf and stem tissue: aphids, wasps, midges (Figure 4–35).
    • Damaged or split twigs: egg laying (oviposition), treehoppers and cicadas (Figure 4–36).

Distinguishing Between Plant Damage Caused by Insects, Diseases and Environmental Stress

 

One way to begin the diagnostic process is to determine if the problem stems from biotic (living) factors, including insects and diseases, or abiotic (nonliving) factors including environmental stress. Examine the patterns of damage, location, and progression to determine whether the cause is biotic or abiotic. Look for signs of a living culprit to distinguish between insect and disease causal agents. Use Table 4–3 as a diagnostic tool.


Table 4–3. A diagnostic tool to help determine the cause of plant damage.
Biotic problems include insects, diseases, weeds, nematodes, parasitic plants, animals, and other living organisms.Abiotic problems include water issues, compacted soil, nutrient deficiencies and toxicity, salinity, pH, temperature, sunburn, light, wind, pollution, lightening, root girdling, mechanical injury, chemical injury, and other nonliving plant problems.

 

BIOTIC (Living)ABIOITIC (Non-Living)
InsectDiseaseWeather, Mechanical, Chemical
LocationGenerally limited to one type of plant (specific host)Generally limited to one type of plant (specific host)Affects multiple types of plants in a specific location
ProgressionOver time progresses on plant and to similar plantsOver time progresses on plant and to similar plantsDoes not progress
SignsFrass, cast skins, insectFungal spores, bacterial oozeNo signs of living pathogen

COMMON MISTAKES IN PEST DIAGNOSIS

 

If all plant pests were always in the most easily identifiable stage, diagnosis would be simple. However, all 1,700 potential pests of ornamentals in North Carolina have egg stages and immature stages that may be difficult to identify. Following are two examples of common mistakes.

 

Lady beetle pupa—The pupae of lady beetles attach themselves by the hind end to leaves or twigs. These pupae do not resemble adult lady beetles (Figure 4–37). A home gardener might assume that they are “sucking the life” out of the plant. Quite to the contrary, however, lady beetles help the plant by eating harmful aphids. Each pupa destroyed by a mistaken diagnosis allows thousands of aphids to survive.

 

Seed-corn maggot flies—Each spring home gardeners discover dead flies on the tips of dogwood and crape myrtle twigs. These flies are infested with an Entomophthora fungus, which “programs” the fly to land on a prominent perch (such as a dead twig) to die. Then the fungus fruits (sporulates) and the spores disperse to infect other flies. The fungus is beneficial because it attacks seed-corn maggots, which consume the inside of seeds, forcing many gardeners to replant. Because the flies often select bare twigs on which to make their last landing, home gardeners sometimes jump to the conclusion that the fly is harming the twig.

 

Submitting Insect Samples to the Plant Disease and Insect Clinic

 

If insect identification is not possible, consult the Extension agent in your county. If you still need help, submit a specimen to the Plant Disease and Insect Clinic at N.C. State University.

 

Follow these instructions:

  • Most insects—roaches, termites, bugs, beetles, flies, wasps, ants, maggots, and spiders preserve in 70 % alcohol.
  • Mites, scales, aphids, and thrips—Send in alive on some part of the affected plant. Place the plant in a plastic bag.
  • Butterflies and moths—Send in dead. Adults can be frozen or put in a kill jar using ethyl acetate fumes. (Nail polish remover contains ethyl acetate.)
  • Caterpillars—Send in alive on some part of the host plant in a plastic bag.
  • Grubs—Send in alive in a pint or two of soil enclosed in a plastic bag.
  • When in doubt, put specimens in 70% alcohol.
  • Collect several specimens if possible.

If a specimen cannot be collected, take digital pictures of the insect and damage to the plant. Tips for good photographs:

  • Be sure to include a “scale” item in images, such as a coin or a thumb.
  • Take many photos from several angles with the flash both on and off.
  • Use the “macro” feature (usually a flower symbol) on a camera to zoom in on the details of the insect. A hand lens can sometimes be put in front of the camera lens to increase magnification.
  • Be sure to take close-up images of the head, thorax, and legs, as well as the underside of the insect.
  • Take images of the insect on the plant if possible as well as on a white or dark sheet of paper.
  • If different life stages of the insect are present, take images of all of them.

Fill out an insect identification form. Provide all of the following information:

  • Date specimen was collected. (Date actually found, not the date submitted.)
  • Town and county where specimen was collected. If not found in a town, give the nearest town. This may or may not be the same as the gardener’s address.
  • Name of collector, the person who captured or collected the insect.
  • What was the insect feeding on when collected? If on a plant, specifically name the plant. If not on a plant, name the location, such as windowsill, carport, or closet.
  • List the severity of the damage or infestation.

webworms

Figure 4–27. Fall webworms completely consume leaves.

U.S. Fish and Wilidlife Service-Midwest Region CC BY – 2.0

leaf cutter bee

Figure 4–28. Leaf cutter bees have chewing mouth parts. They cut semi-circles out of leaves, roll them up, and use them line their tubular nesting sites. Leaf cutter bees are beneficial insects and do not damage enough plant tissue to be of concern.

Jack Skipworth, Flickr  CC BY-NC-ND – 2.0

Pear sawfly

Figure 4–29 a. Pear sawfly (is often mistaken for a slug) skeletonizer.

bramblejungle, Flickr  CC BY-NC-ND – 2.0

elm leaf beetle

Figure 4-29 b. Elm leaf beetle skeletonizing a leaf.

Jacinta Llunch Valero, Flickr  CC BY-NC-SA – 2.0

leaf miners

Figure 4–30. Leaf miners tunnel through the upper and lower leaf surfaces.

Scot Nelson, Flickr  CC BY – 2.0

aphid damage

Figure 4–31. Aphid damage created areas of bleached stippling on this leaf.

Scot Nelson, Flickr  CC BY – 2.0

spidermite damage

Figure 4–32. A random stippling pattern created by the piercing-sucking mouthparts of spidermites.

Scot Nelson, Flickr  CC BY-NC-SA – 2.0

hemlock wooly adelgid

Figure 4-33. Hemlock woolly adelgid (Adelges tsugae),is an exotic insect pest that has wreaked havoc on forest and stream ecosystems across eastern North America. Small, white, cottony sacs at the base of the needles indicate the insects’ presence.

Nicholas A. Tonelli, Flickr CC BY – 2.0

thrip damage tomato

Figure 4–34. Thrips damage on a tomato plant. Thrips use their rasping sucking mouth parts to feed damaging leaves. As the leaves mature and mature the scar tissue causes them to curl.

Katie Mims, Flickr  CC BY-NC-ND – 2.0

mite gall

Figure 4–35. Galls on cherry leaves caused by the mite Eriophyes tiliae.

Jason Hollinger, Flickr  CC BY – 2.0

oviposition wound

Figure 4–36. Oviposition wounds on a twig.

Armed Forces Pest Management Board, Flickr CC BY-NC-ND – 2.0

ladybeetle stages

Figure 4–37. Stages of ladybeetle development: the small black larva develop into larger black/orange larva. These larvae are dining on aphids. In the center is the ladybeetle pupa.

Jill Siegrist, Flickr  CC BY-NC-SA – 2.0

 

Types of Insect Injury

 

Chewing Insects

 

Some insects feed by chewing external parts of a plant. To get an idea of how prevalent this type of insect damage is, try to find leaves of plants that have no sign of injury from chewing insects. Cabbageworms, armyworms, grasshoppers, Colorado potato beetles, and fall webworms are common examples of insects that cause injury by chewing.

 

Piercing-Sucking Insects

 

Another way insects feed on growing plants is by piercing the epidermis (skin) and sucking sap from cells. These insects have a slender, sharp, pointed portion of their mouthparts that they thrust into the plant and suck up plant sap. The hole is so small it is not easy to see. The withdrawal of sap causes minute white, brown, or red spots on leaves, fruits, or twigs. This often results in curled leaves, deformed fruits, or general wilting, browning, or death of the entire plant. The spots remain after management, but new foliage should be normal. Aphids, scale insects, squash bugs, leafhoppers, and plant bugs are examples of piercing-sucking insects. The difference between chewing and piercing-sucking damage can be seen in Figure 4–38.

 

Internal Feeders

 

Some insects feed within plant tissues during all or part of their destructive stages. They gain entrance to plants in the egg stage either when their mothers deposit eggs into the plant tissue or the nymphs after hatching from the eggs, eat their way into the plant. In either case, the hole of entry is usually minute. A large hole in a fruit, seed, nut, twig, or trunk generally indicates where the insect has come out, not where it entered.

 

Common group names for internal feeders include borers in wood or pith; worms or weevils in fruits, nuts, or seeds; leaf miners; and gall insects. Nearly all of the internally feeding insects live inside the plant during only part of their lives and usually emerge as adults. Leaf miners (Figure 4–39) are small enough to find comfortable quarters and an abundance of food between the upper and lower epidermis of a leaf. Management strategies are most effective when aimed at emerging adults or during the immature stages before they enter the plant.

 

Belowground Feeders

 

Belowground feeders include chewers, sap suckers, root borers, and gall insects. Their attacks are the same as aboveground pests, except that they harm plant parts below the soil surface. The woolly apple aphid, for example, as both nymph and adult, sucks sap from roots of apple trees, causing the development of tumors and subsequent decay of the tree’s roots. With other belowground insects, the larvae are root feeders, but the adults live aboveground. Examples of belowground feeders include wireworms, root maggots, pillbugs, strawberry root weevils, and grape and corn rootworms.

 

Egg Layers

 

Insects can damage plants by laying eggs in critical plant tissues. The periodic cicada, for instance, deposits eggs in one-year-old growth of fruit and shade trees, splitting the wood so severely that the entire twig often dies. As soon as the young hatch, they leave the twigs. Though the dead branches can seem alarming, most established trees will withstand the damage. Pruning out damaged branches would be the only management necessary.

 

Some insects cause plants to produce a structure of deformed tissue called a gall (Figure 4–35). The insect then finds shelter and abundant food inside this plant growth. The growth of the gall occurs when an adult lays an egg inside plant tissue; the gall develops through reactions with the secretions of the developing larva. A gall-forming insect can cause galls on different plants, but the galls will be similar in appearance. If several species of gall-forming insects attack the same plant, the galls that form will differ in appearance. Although the gall is made entirely of plant tissue, the insect controls and directs the form and shape the gall takes as it grows. While galls may be unsightly, they generally do not cause problems for healthy plants.

 

Nesting Insects

 

Besides laying eggs in plants, insects sometimes remove parts of plants for the construction of nests. Leaf-cutter bees nip out neat, circular pieces of foliage, which they carry away and fashion together to form thimble-shaped cells. Some insects fold, roll, or tie leaves together for a protective cover. While it may be disturbing to see some leaves cut or missing from a plant, the damage is often minimal and does not require management.

 

Vectors of Plant Disease

 

There is evidence that insects spread more than 200 plant diseases. About 150 diseases are caused by viruses, 25 or more by parasitic fungi, 15 or more by bacteria, and a few are caused by protozoa.

 

Insects may spread plant diseases in the following ways:

  • Indirectly when they feed, lay eggs, or bore into plants, creating an entrance point for a disease present in the environment.
  • Directly on or in their bodies as they move from one plant to another susceptible plant.
  • Directly as they feed on susceptible plants, they infect them with the disease organism.
  • Indirectly as an essential host for some part of the pathogen’s life cycle, and the disease could not complete its life cycle without the insect host.

Table 4–4. Some Plant Diseases Carried by Insects

DiseaseInsect Carrier
Dutch elm disease (fungus)small beetle
Fire blight (bacterial)pollinating insects
Tomato curly top (virus)beet leafhopper
Tomato spotted wilt (virus)Western flower thrips
Watermelon mosaic virusaphids

Honeydew Producers

 

Honeydew is a sweet, sticky liquid excreted by insects that feed on sap from the phloem tissue of plants. Aphids, mealybugs, soft scales, and planthoppers feed on phloem by sucking with slender, threadlike mouthparts. Sap from phloem is rich in sugar but poor in other nutrients, so these insects consume large amounts of sap to obtain enough minor nutrients. The pests, therefore, excrete copious amounts of honeydew. Unless washed off by rain, honeydew clings to the plant and surfaces below it.

 

Honeydew itself is not a harmful substance. However, spores or fragments of dark fungi called sooty mold are blown or carried to the honeydew, and new colonies of sooty mold develop. Many times the tiny strands of sooty mold become so abundant that infested plants appear dark and sooty or almost charcoal gray. The mold can block sunlight to the point that photosynthesis is no longer possible. Heavily infested leaves often die. Feeding by a large number of aphids or scales combined with the heavy coating of sooty mold may drastically reduce the vigor and beauty of ornamental plants.

 

chewing piercing sucking

Figure 4–38. Chewing damage to a kale leaf, likely from the chewing mouthparts of a beetle (left), and stippling on a bean leaf from the piercing-sucking mouthparts of a lace bug (right).

Scot Nelson, Flickr  CC BY – 2.0

leafminer stages

Figure 4–39. Stages of a leafminer. Eggs are deposited on the surface of a leaf, they become larvae that tunnel through the leaves leaving frass (middle). They pupate and emerge as adult flies..

Martin Cooper Ipswich, Flickr  CC BY – 2.0

 

Encouraging Beneficial Insects

 

Take advantage of biological management in a garden by encouraging natural predators such as praying mantids, lady beetles, lacewings, and ground beetles. Increase their populations by providing shelter, food, moisture, and overwintering sites. Some beneficial insect suppliers offer a formulation for feeding and attracting the beneficials to keep them in the garden longer.

 

Learn to recognize the eggs and larvae of the beneficial insects, and avoid harming them. Praying mantid egg cases are often found in weedy lots. Carry the twig with the cluster attached into the garden and set it in a place where it will not be disturbed. Learn to recognize parasites and their egg cases. For example, the tomato hornworm often has a number of white cocoons, a little larger than grains of rice, on its back. These are from a parasitic wasp. The hornworm will die, and more wasps will emerge. Obviously, it is to a gardener’s advantage to leave that caterpillar in the garden.

 

Another possibility is to increase the type and number of plants in a landscape that will attract beneficial insects. Search for beneficial insects in the NC State Plant Database. Most composite and umbel plants attract beneficial insects by providing nectar and pollen that prolong the insect’s life. Cosmos and marigolds attract a few beneficial insects, and tansy attracts large numbers. Best results come from planting the attractant plants on the edges of the area instead of interplanting them in the garden.

 

Insecticides often kill beneficial insects. A selective insecticide has less adverse effect than a broad­spectrum insecticide. Stomach poison insecticides are less likely to harm beneficial insects. Apply insecticides at dusk, as this is the time when most beneficial insects are done foraging for nectar or pollen.

 

Table 4–5. Plants that attract beneficial insects.

PlantInsects
Black locustLady beetles
CarawayLacewings, hover flies, insidious flower bugs, spiders, parasitic wasps
Common knotweedBig-eyed bugs, hover flies, parasitic wasps, soft-winged flower beetles
CowpeaParasitic wasps
Crimson cloverMinute pirate bugs, big-eyed bugs, lady beetles
Flowering buckwheatHover flies, minute pirate bugs, predatory wasps, tachinid flies, lacewings, lady beetles
Hairy vetchLady beetles, minute pirate bugs, predatory wasps
Queen Anne’s laceLacewings, predatory wasps, minute pirate bugs, tachinid flies
SpearmintPredatory wasps
Sweet alyssumTachinid flies, hover flies, chalcids, wasps
Subterranean cloverBig-eyed bugs
Sweet fennelParasitic wasps, predatory wasps
TansyParasitic wasps, lady beetles, insidious flower bugs, lacewings
White sweet cloverTachinid flies, bees, predatory flies
Wild buckwheatHover flies, minute pirate bugs, tachinid flies
YarrowLady beetles, parasitic wasps, bees
a Other plants that attract a variety of beneficial insects include sage, wallflower, salvia, nasturtium, poppy, zinnia, dill, anise, fennel, coriander, parsley, marigold, aster, daisy, coneflower, bee balm, basil, oregano, mint, cosmos, lovage, wild mustard and canola.

 

Case Study—Think about IPM: A Cantaloupe Problem

You are concerned about your cantaloupe plant. The vines are doing poorly, some of the fruit has scarring, and you are concerned you will lose the whole crop. You review the diagnostic procedures from chapter 7, “Diagnostics“, and think about the five steps for IPM:

 

  1. Monitor and scout insects to determine insect type and population levels.
  2. Accurately identify pest and host.
  3. Consider economic or aesthetic injury thresholds. A threshold is the point at which action should be taken.
  4. Implement a treatment strategy using physical, cultural, biological, and/or insecticide control.
  5. Evaluate success of treatments.

1. Monitor and determine insect type

You have noticed the plants not doing well for a few weeks. An insect that looks like a beetle has been flying around the crop. The plants have been in the ground for a few months (are mature) and they appear to have insect damage to their leaves. A younger planting of the same crop suffered from severe damage, and the stems appeared chewed through. Cantaloupe has been planted in the same spot for many years. You feel the insect population is high enough and damage is severe enough to warrant further investigation. You take a sample of the leaves getting leaves that are healthy, partially affected and completely affected by damage. You also try to capture the insect if possible or at least get some good photographs. You review the sample collection information found in the “Submitting Insect Samples to the Plant Disease and Insect Clinic” section of this chapter.

 

2. Accurately identify the pest and host

Using the samples you research this problem. The leaves appear to be missing sections, especially along the margins, which leads you to believe an insect with chewing mouthparts was present. You carefully examine the sample to see if any insects are still present. You see a yellow and black insect and remove it from the plant for further investigation. The insect is quite active, so you put it in a jar and freeze it to slow it down. Looking at it with your hand lens, you determine it is in the order Coleoptera, or a beetle, because you see two pairs of wings; the outer pair is hardened or leathery with yellow and black stripes, and the inner pair is membranous and folds under the front wings. You also see chewing mouthparts and long jointed antennae. You consult some insect identification guides at the Extension office and discover a photo that looks like your insect (Figure 4–40). You read that cucumber beetles can attack all plants in the cucurbit family and that cantaloupe is in that family. Now that you have a positive ID, you do more research on this insect. You type in “cucumber beetle + extension” into your Internet search engine.

 

3. Consider economic or aesthetic injury thresholds

The injury to these vines and their fruit is severe enough to warrant management. It may be too late for this year’s crop, but you can research how best to avoid this problem in future plantings.

 

4. Implement a treatment strategy using physical, cultural, biological, and/or insecticide control

You research cultural strategies to discourage cucumber beetles. Cucumber beetle eggs often overwinter in discarded plant material, so removal of plant material after the growing season and plowing or turning the planting bed will help disrupt this part of the beetle’s life cycle. Crop rotation can be an effective means of managing soil fertility and pest problems. Ideally, plant a different crop family in the spot, waiting at least three years before returning to a cucurbit family crop. The use of resistant varieties is perhaps the most important management tactic. The following cucurbit varieties are resistant to cucumber beetles as seedlings and also have resistant foliage later in the season: Blue Hubbard (squash); Ashley, Chipper, Gemini (cucumber). Use of resistant varieties may not give complete control where infestations are heavy. The NC Cooperative Extension publication AG-295, Insect and Related Pests of Vegetables, gives additional cultural management strategies.

 

Delaying planting times for more favorable germinating conditions and heavy seeding rates will ensure a good stand. For young seedlings, wire or cloth screen protectors shaped like cones will keep beetles off home plantings until plants are established.

 

If this combination of management strategies is not enough, insecticides may be needed. In that case, a foliar insecticide applied at the cotyledon stage will retard cucumber beetle feeding and encourage plant establishment. Where insects are abundant, additional foliar applications may be needed to prevent beetles from spreading bacterial wilt and squash virus. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

 

5. Evaluate success of treatments

You decide to keep a garden journal or notes about management strategies tried and their results. You realize that it may take more time to see the results of some strategies than others.

 

cucumber beetle

Figure 4-40. A striped cucumber beetle, Coleoptera order.

Matt Bertone

 

Frequently Asked Questions

  1. There are spots on my leaves. How can I tell if they are caused by an insect or disease? The first step is accurately identifying the plant. Many insects and diseases are host specific. It is also important to consider any abiotic factors that could cause damage to your plant or leave it susceptible to insects or disease. Is it possible the plant is drought stressed or had herbicide overspray contact the leaves? Has anything in the environment changed recently? Was the plant recently fertilized? Where are the damaged leaves—all over the plant or only on new growth? Are there any wounds on the plant? Ask probing questions and find out as much history on the plant as you can. Insect damage to plants comes from either chewing, sucking, or boring. Indications that insects with chewing mouthparts are feeding on your plants include missing chunks of leaves or stems, skeletonization of leaves or leaf mining. Insects with sucking mouthparts remove sap from plant cells, which can cause stippling (spotting), discoloration, or drooping of leaves, or lead to honey dew. Boring insect larvae tunnel into the plant beneath the bark, leaving sawdust toothpicks on tree trunks or sawdust mounds below. Their adult forms can feed on leaves or twigs. You may look for the insects themselves, insect parts, or frass (excrement). Some fungal diseases can leave spots on leaves. The diseases generally produce “target-like” spots, each with a dark center, yellowing ring, and a brown or red margin between the dead tissue and the live green tissue of the plant.
  2. There are small bumps on the leaves of my hackberry, is it going to die? You would need to see a sample or a photograph, but this is most likely insect galls. Galls are abnormal growth of plant cells due to an injection of a chemical by an adult or larval form of an insect. These chemical causes the plant tissue to swell and become misshapen, forming the bumps you see. Insects often live inside the galls for a short period of time, gaining shelter from predators and feeding off the swollen plant tissue. Galls are quite common on plants like hackberry and oaks. The damage, generally cosmetic, will not kill the plant.
  3. There are many black bugs with orange stripes on their backs flying around in my grass. It looks like somebody spit on my grass in spots.These are most likely two-lined spittlebugs. Both adults and nymphs damage turf by sucking out the plant juices from leaves and stems. They also produce a spittle mass, which is nothing more than a nuisance. In late summer adults can also fly to hollies to feed and cause holly leaves to drop prematurely. Following good turf management practices, reducing excessive thatch, and avoiding overwatering will help manage spittlebugs. Plant a more tolerant turfgrass species such as St. Augustinegrass or zoysiagrass, and avoid centipedegrass if possible. On ornamentals and grape vines, a strong spray of water may be sufficient for management.
  4. How do I get rid of fire ants? Red imported fire ants expand naturally and steadily in our area because their reproductive rates are high and our winters are mild. The mounds are unsightly, and their stings are painful. Both baits and contact insecticides are effective management tools. Common active ingredients are hydramethylnon, spinosad, methoprene, and pyriproxyfen. In bait formulations the active ingredients are shared by the ants in a mound, including the queen (which is the only ant in the colony that can lay eggs), usually resulting in more effective management. Contact products containing the active ingredients acephate, carbaryl, or pyrethroids produce management in a few days if broadcast over the landscape, or in a few hours if applied to individual mounds. Both require water (rainfall or irrigation) to become active. An exception is a product with the active ingredient fipronil, which produces long lasting effects when broadcast in late May to early June. Fipronil will provide five to six months of management. Repeat treatment in November if ant mounds reappear in the fall, as sometimes happens. Be sure to read and follow product labels closely before application in order to achieve desired results. To determine if you have fire ants, look for two nodes between the thorax and abdomen. Other ants only have one. For more information regarding fire ant management in the home landscape type “fire ants + extension” into your internet search engine.

If you have questions about this chapter contact your local NC State Extension Expert at your county’s NC State Extension Center.

 

Further Reading

Bellows, Thomas S. and T W. Fisher, eds. Handbook of Biological Control: Principles and Applications of Biological Control. San Diego, California: Academic Press, 1999. Print.

Brandenburg, Rick L. and Callie P. Freeman, eds. Handbook of Turfgrass Insects, Second Edition. Annapolis, Maryland: Entomological Society of America, 2012. Print.

Bruneau, Arthur H. and Gail G. Wilkerson, eds. Turfgrass Pest Management Manual: A Guide to Major Turfgrass Pests & Turfgrasses. Raleigh, North Carolina: North Carolina Cooperative Extension Service, 2006. PDF file.

Capinera, John L. Handbook of Vegetable Pests. San Diego, California: Academic Press, 2001. Kindle file.

Clark, Christopher A., et al., eds. Compendium of Sweetpotato Diseases, Pests, and Disorders. 2nd ed. St. Paul, Minnesota: The American Phytopathological Society, 2013. Print.

Common Tree Fruit Pests. Columbia, Missouri: University Of Missouri Extension, 1993. Print. North Central Regional Publication NCR 63

Cottam, Clarence, and Herbert S. Zim. A Golden Guide from St. Martin’s Press: Insects. New York: St. Martin’s Press, 2002. Print.

Cranshaw, Whitney. Garden Insects of North America. Princeton, New Jersey: Princeton University Press, 2004. Print.

Davidson, Ralph H., and William F. Lyon. Insect Pests of Farm, Garden, and Orchard. 8th ed. Hoboken, New Jersey: John Wiley & Sons Inc., 1987. Print.

Dreistadt, Steve H. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. 2nd ed. Davis, California: University of California Division of Agriculture And Natural Resources, 2004. Print. Publication 3359.

Ellis, Barbara W. and Fern Marshall Bradley, eds. The Organic Gardener’s Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy without Chemicals. Emmaus, Pennsylvania: Rodale Press, Inc., 1996. Print.

Ellis, M. A., et al., eds. Compendium of Raspberry and Blackberry Diseases and Insects. St. Paul, Minnesota: The American Phytopathological Society, 1991. Print.

Elzinga, Richard J. Fundamentals of Entomology. 6th ed. Upper Saddle River, New Jersey: Prentice Hall, Inc., 2004. Print.

Horst, R. Kenneth, and Raymond Cloyd. Compendium of Rose Diseases and Pests. 2nd ed. St. Paul, Minnesota: The American Phytopathological Society, 2007. Print.

Johnson, Warren T., and Howard H. Lyon. Insects That Feed on Trees and Shrubs. 2nd ed. Ithaca, New York: Cornell University Press, 1991. Print.

Jones, Jeffrey B., et al., eds. Compendium of Tomato Diseases and Pests. 2nd ed. St. Paul, Minnesota: The American Phytopathological Society, 2014. Print.

Leahy, Christopher. Peterson First Guide to Insects of North America. New York: Houghton Mifflin Company, 1998. Print.

Mitchell, Robert T., and Herbert S. Zim. Butterflies and Moths: Revised and Updated. New York: St. Martin’s Press, 2002. Print.

Pirone, Pascal P. Diseases and Pests of Ornamental Plants. 5th ed. New York: John Wiley & Sons, Inc., 1978. Print. Note: This is a good resource for diagnostics; refer to the North Carolina Agricultural Chemicals Manual for the latest chemical information.

Schultz, Warren, ed. Natural Insect Control: The Ecological Gardener’s Guide to Foiling Pests. 1995. Brooklyn, New York: Brooklyn Botanic Garden, 1999. Print.

Schwartz, Howard F. and S. Krishna Mohan, eds. Compendium of Onion and Garlic Diseases and Pests, Second Edition. St. Paul, Minnesota: The American Phytopathological Society, 2008. Print.

Solomon, J. D. Guide to Insect Borers in North American Broadleaf Trees and Shrubs. Washington, DC: United States Department of Agriculture Forest Service, 1995. PDF file. Agriculture Handbook AH-706.

Sutton, Turner B., et al., eds. Compendium of Apple and Pear Diseases and Pests. 2nd ed. St. Paul, Minnesota: The American Phytopathological Society, 2013. Print.

Weinzierl, Rick, and Tess Henn. Alternatives in Insect Management: Biological and Biorational Approaches. Urbana, Illinois: University of Illinois At Urbana-Champaign, 1991. PDF file. North Central Regional Extension Publication 401.

Weinzierl, Rick, and Tess Henn. Alternatives in Insect Management: Microbial Insecticides. Urbana, Illinois: University of Illinois At Urbana-Champaign, 1989. PDF file. Circular 1295.

Weinzierl, R., et al. Insect Attractants and Traps. Gainesville, Florida: University of Florida Institute of Food And Agricultural Science, 2005. PDF file. Publication ENY-277.

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Thrips – Pest

Pests & Diseases: Thrips

Thrips – Pests & Diseases

Thrips are recognizable by their small size and long flat shape. The adult thrips has four feathery wings. They can vary in color from gray to yellow or brown. Thrips are carriers of viruses, mainly of the genus Tospovirus. These viruses cause significant crop loss and are incurable.
 

About the pest in brief

 

What are Thrips?
When we use the term thrips, we are referring to a wide group of insects of the order Thysanoptera.
What can you see?
Because certain toxic substances are present in the saliva of thrips, you may see some deformations in the shoots or flowers of the affected plants.
What can you do?
Spray plants with ecological insecticides like potassium soap or plant extracts with pyrethrum.

Biological cycle of thrips

 

The first stage of the thrips’ life cycle is the egg, which will hatch much more quickly when temperatures are higher. The females lay eggs in plant tissues. The larvae that emerge from the eggs feed on the surrounding tissues. One of the characteristics of these insects is that they make the transition from pupa to adult in the soil or in the lower leaves. The larvae live in the leaves, but as soon as they reach the right stage of development, they fall to the ground or lower leaves where they live during the pre-pupal and pupal stages until a reproductive adult appears with fully developed wings. The whole life cycle lasts only a few weeks.

 

Thrips

 

Symptoms of the pest

The adult thrips eats a varied diet based mainly on pollen, but the larvae feed on plant tissues and it is the larvae that are responsible for the majority of plant damage. The larvae suck the liquid from plant cells, mainly from the leaves, but also the petals, shoots and fruits. Early symptoms include an almost transparent or clear discoloration of the leaf with black dots (which are caused by fecal secretions). They have rasping, sucking mouthparts that look like combs and make a soup from the tissue which is then sucked up. Usually the top layer of the tissue is undisturbed and a window of clear tissue is seen in the middle of the area of discoloration.

 

Because certain toxic substances are present in the saliva of thrips, some deformations may occur in the shoots or flowers of affected plants. In cases of very severe infestation, the leaves may dry up entirely. At the same time, some thrips like Frankliniella occidentalis secrete a few drops of a substance when they are threatened by predators. These excretions contain decyl acetate and dodecyl acetate – pheromones that serve as a warning signal for other nearby thrips.

 

How to prevent the pest?

 

Because of the thrips’ ability to transmit viruses, it is important to monitor our crops for thrips and detect them as early as possible. The classic method for doing this is by using adhesive traps. These traps are blue in color, because thrips are strongly attracted to blue. The traps should be examined every few days using a magnifying glass to see if any thrips (usually winged adults) have gotten stuck to them.

 

Thrips

 

Solutions for controlling the pest

 

If you detect thrips, appropriate treatments need to be administered to minimize the risk of an infestation. These treatments include ecological insecticides such as potassium soap or plant extracts with pyrethrum, in places where these are allowed by law. Plants must be sprayed thoroughly all over because the thrips will take refuge under the veins of the leaves, making it difficult for the insecticide to come into contact with all the insects.

 

It is also possible to use entomophagous fungi to combat thrips. Beauveria bassiana is one fungi that is typically used to combat thrips. It is also important to make sure that you clean up and remove any plant or soil residues from the floor or worktops.

Aphids – Pest

 Aphids – Pests & Diseases

Aphids are no longer than about 4 mm, have a bulbous abdomen and can be many different colors. They are among the most destructive pests to affect cultivated plants in temperate regions. Winged aphids are especially dangerous for your crops, since they destroy plants much faster than regular aphids
 

About the pest in brief

What are aphids?
When we refer to aphids, or plant lice, we usually mean a super family of insects which includes over 4.000 species of plant-specific parasites.
What can you see?
Aphids can cause decreased growth rates, mottled leaves, yellowing, stunted growth, curled leaves, browning, wilting, low yields and death in plants.
What can you do?
There are several cultivation techniques that we can use to prevent or minimize an attack of aphids.

Biological cycle of aphids

Aphids can be winged or wingless. Usually, the first generation to hatch after winter is wingless. However, after several generations there can be a lack of space on the host plant. This triggers the birth of a generation of winged aphids, which can migrate to other hosts. All the aphids born from the winter eggs are females. Several more generations of female aphids are born during spring and summer. Females can live for 25 days, during which they can each produce up to 80 new aphids. Spring and summer reproduction occurs asexually – without males.

Aphids

Symptoms of the pest

The aphids feed on phloem sap, which weakens the plant and causes a metabolic imbalance, twisting of the leaves and, in extreme cases, causing leaf loss. Leaf loss affects the quantity and quality of the final harvest. Aphids also introduce toxins into the plant, systemically altering its development.

Furthermore, the honeydew secreted by the aphids is an ideal culture medium for a range of various fungi, which form a barrier on the leaf, stopping it from taking in all the light that hits it.

However, the most harmful effect of aphids is the transmission of viruses. Aphids can transmit dozens of viruses from a diseased plant to healthy one in just a few seconds, especially the winged generations. The biggest problem with viruses is that there is no remedy for them, so the infection of a plant that is not tolerant or resistant to the virus leads inevitably to a decline in the final production.

Aphids

CONTROL AND PREVENTION

HOW TO GET RID OF APHIDS

  • Try spraying cold water on the leaves, sometimes all aphids need is a cool blast to dislodge them.
  • If you have an aphid invasion, dust plants with flour. It constipates the pests. 
  • Use commercially available biological controls or by spraying with insecticidal soap or horticultural oil.
  • You can often get rid of aphids by wiping or spraying the leaves of the plant with a mild solution of water and a few drops of dishwashing detergent such as Ivory.
  • Stir together 1 quart of water, 1 tsp of liquid dish soap and a pinch of cayenne pepper. Do not dilute before spraying on plants.
  • Organic controls include soapy emulsion, horticultural oil (read the directions), and pyrethrum spray. Soapy water should be reapplied every 2-3 days for 2 weeks.
  • Use homemade garlic or tomato-leaf sprays.

There are several cultivation techniques that we can use to prevent or minimize an infestation of aphids.

These include:

  • Eliminating weeds that can serve as a reservoir of eggs and adults
  • Using insect nets (sometimes insecticide-impregnated) to cover crops
  • Avoiding the excessive use of nitrogenous fertilizer
  • Removing crop residues
  • Establishing plant species that can serve as a reservoir for predators (banker plants)

PREVENT APHIDS

  • For fruit or shade trees, spray dormant oil to kill overwintering eggs.
  • You can purchase beneficial insects, such as lady beetles, lacewings, and parasitic wasps, which will feed on aphids. These are usually ordered via mail—check the Internet for labs. They should keep the aphid populations controlled in the first place.
    • You can also plant flowering groundcovers in home orchards to attract predators.
  • Companion planting can be very helpful to keep aphids away from your plants in the first place. For example:
    • Aphids are repelled by catnip.
    • Aphids are especially attracted to mustard and nasturtium. You can plant these near more valuable plants as traps for the aphids. 
    • Nasturtiums spoil the taste of fruit tree sap for aphids and will help keep aphids off broccoli.
    • Garlic and chives repel aphids when planted near lettuce, peas, or rose bushes. 

Solutions for controlling the pest

The natural enemies of aphids include ladybird beetles (or ladybugs) and lacewings. Green lacewing larvae (Chrysoperla sp.) are voracious predators of aphids.