Garden Insect Primer: Getting to Know Common Garden Insect Pest Groups and their Associated Signs of Plant Damage

by Bruce Wenning

There are 31 orders of insects, but of those only 11 orders contain economically important pests of trees, shrubs, garden plants, lawns, vegetable crops, wood, and fiber. Most of the insect damage caused to garden plants plaguing garden maintenance people and garden designers are concentrated in just seven orders.

Familiarity of insect pests of garden perennials and annuals and associated beneficial insects can be important to ecological landscape designers because this knowledge may influence garden plant pollination availability, plant selection and placement, and other considerations pertinent to low maintenance ecological design.

Getting acquainted with insect pests can be a daunting task. As mentioned above, most of the garden and landscape insect pests are in just seven orders (i.e. species specific taxonomic groups). This article presents some important insect order characteristics and examples of common pest damage signs frequently seen on woody and herbaceous garden plants.

Brief Arthropod Classification

Below is a brief (not complete) taxonomic listing of commonly seen garden arthropods and other invertebrate groups inhabiting gardens. This article will focus on the larger groups and associated plant damage. Only certain species from each group (i.e. order) will be presented as examples. All species discussed are part of the Arthropoda phylum as listed in Borer, Triplehorn and Johnson (1989).

Phylum: Arthropoda (jointed foot). Arthropods

Subphylum: Chelicerata. Have six pairs of appendages. The first pair are chelicerae, the rest are leg-like.

Class: Arachnida. (Spiders, harvestmen and adult mites have eight legs)

Order: Araneae (spiders)

Order: Opilliones (harvestmen – Daddy-Longlegs)

Order: Acari (mites and ticks). Some mites are plant pests.

Subphylum: Crustacea. Crustaceans

Class: Malacostraca

Order: Isopoda–sowbugs

Subphylum: Atelocerata

Class: Diplopoda. Millipedes (have 30 or more pairs of legs)

Class: Chilopoda. Centipedes (have 15 or more pairs of legs)

Class: Pauropoda. Pauropods (have nine pairs of legs)

Class: Symphyla. Symphylans (have 10 to 12 pairs of legs)

Class: Hexapoda. Insects (six foot) – The Insects are primarily divided up into orders on the basis of adult wing structure; mouthparts; other bodily characteristics of adults and/or larvae, such as antennae and leg structure, bristle number and arrangement, and other morphological details; and type of metamorphosis. Insects have three body regions (head, thorax, and abdomen), antennae, and six legs.

Phylum: Mollusca. Slugs and snails are mentioned here because some are pests in gardens.

Brief Insect Pest Morphology and Development

First, let’s get some basic physiology and development out of the way. Insects have three distinct body regions: head, thorax, and abdomen.

  • The head is sensory containing the mouth for feeding, antennae for chemical detection, and the eyes (or eye complex) for light detection and limited image perception.
  • The thorax is the region of major muscles for movement of the legs and wings. Legs and wings are always connected to the thorax in all insects.
  • The abdomen functions in reproduction, digestion, waste elimination, and breathing. That’s right, insects breathe through their abdomens by way of spiracles (minute openings in the abdomen for oxygen intake) (Borer et al, 1989).
fig-1-ela-fact-sheet-12-grasshopper-model-body-plan-7395473_orig

Figure 1. Adult insect body plan.

Figure 1 illustrates the adult insect body plan using the grasshopper as a model. Notice that the wings cover the abdomen. For all winged adult insects, the wings cover or partially cover the abdomen, except dragonflies (Odonata), which hold their wings away from the body at rest.

Metamorphosis

Metamorphosis is the term used for insect development from egg to adult. When an insect egg hatches, the resulting larva (or immature) feeds, grows, and in a short time for most insects, changes into an adult. Again this gradual growth and development from egg to adult is referred to as metamorphosis.

There are two major types of insect metamorphosis: Simple and complete, as illustrated in Figure 2.

fig-2-ela-fact-sheet-12-insect-metamorphosis-0532-figure-2

Figure 2. Examples of complete and incomplete metamorphosis.

In simple or incomplete metamorphosis, the insect progresses from egg, to larva or nymph, and then to adult. The larval stage feeds like the adult (and on the same host plant), but is smaller, lacks fully developed wings, and cannot reproduce. Only adults are capable of reproducing. Figure 3 illustrates this type of metamorphosis.

fig-3-ela%20fact%20sheet%2012%20incomplete%20meta%20flowerbug%20grad_meta_diag

Figure 3. Incomplete (simple) metamorphosis.

In complete metamorphosis, an insect progresses from egg, to larva, to pupa, and then to adult. Figure 4 illustrates how the larva is very different in appearance from the adult. The extra developmental stage called the pupa allows for more complex development of the insect into the adult stage. An insect in its pupa stage is very different from the larval stage in size, occupied habitat, habit, appearance, and host food plants (in most cases) (Borer et al, 1989). The pupa does not feed.

Figure 4. Incomplete metamorphosis.

Figure 4. Complete metamorphosis of a butterfly.

For example, butterflies (order Lepidoptera) experience complete metamorphosis: egg, larva, pupa, adult. Figure 5 shows this adult butterfly emerging from its pupal case. In the Lepidoptera (butterflies and moths), caterpillars are the larval stage which are “eating machines” on plant leaves, but the adults feed on nectar. Beetles (Coleoptera) also undergo complete metamorphosis. The white grub, European chafer (Rhizotrogus majalis) feeds on lawn roots and devastates home lawns if not controlled, but the adult rarely is injurious to plants (Vittum, Villani and Tashiro, 1999). Understanding insect pest metamorphosis is important in identifying pest control options and techniques.

Figure 5.

Figure 5. The adult butterfly emerges from its pupal case.

The larval stages in both types of metamorphosis have several growth stages called instars.

The Major Pest Orders and Associated Signs of Plant Damage

The insect pests most commonly encountered on perennial and annual garden plants are found in seven insect groups, or insect orders; however, there are many species in each order. For example, in the order, Coleoptera (beetles), there are many species of plant pests, as well as species of predators and decomposers. The insect pests in the orders presented here produce characteristic plant damage with few similarities between orders. Similar plant damage caused by different orders will be noted.

Order: Thysanoptera (Thrips)

Most thrips species are plant feeders. Some thrips are leaf and flower pests. They are minute (one millimeter wide and three to four millimeters long) and mobile insects with slender, torpedo-shaped bodies. (See Figure 6.) They can be difficult to see without a magnifying glass or microscope. Four wings may be present or absent in the adults. If present, they are fringed. Mouthparts are the rasping-sucking type. Metamorphosis is more complex for insects in this order than for insects in the other orders presented below and is between simple and complete because the third instar is a prepupa and the fourth instar is the pupa. (See Figure 7.) When thrips populations are large, plants can be damaged severely because larvae and adults feed on the same host plant at the same time!

Figure 6. Thrips are tiny insects.

Figure 6. Thrips are tiny and difficult to see without aid.

Figure 7. Thrip life cycle.

Figure 7. Thrips life cycle.

Figure 8. Thrips damage to petunia.

Figure 8. Thrips damage to petunia.

Damage: Thrips cause flower and leaf bud damage as they feed on flower and leaf cellular fluids. Figure 8 illustrates thrips damage to petunias. Much of the damage is done while leaves and/or flowers are in the bud stage and as they unfurl, petals and leaves show a physical distortion. (Refer to Figure 9.) Flowers may also show brown streaks (petal scarring) and leaves and petals may appear distorted with brown or silvery white spots. Rose and peony plants are susceptible to the flower thrips (Frankliniella tritici), as well as to other pest species (Pirone, 1978). Figure 10 shows petal scarring on a rose. Figure 11 shows white flecking damage on tomato due to thrips feeding on leaves. Fecal droppings are frequently present.

Figure 9. Thrips cause leaf distortion.

Figure 9. Thrips damage in the bud stage causes leaf distortion.

Figure 10. Thrips damage to rose petals.

Figure 10. Thrips damage to rose petals.

Figure 11. Thrips damage on tomato plant.

Figure 11. Thrips damage on tomato plant.

Parthenogenesis (egg develops without male fertilization) occurs in many species, including thrips (Borer et al, 1989; Carr, 1979). Parthenogenesis is important in insecticide resistance in response to the over use of nerve poison insecticides. When an insecticide is repeatedly used as the sole method of control, resistance to that compound builds up to the point that some progeny of the resistant parent is now resistant to the insecticide. Parthenogenesis allows for more offspring or all offspring to show insecticide resistance. In other words, one insecticide resistant female can give birth to many resistant offspring, and so on and so on.

Thrips are mostly a greenhouse problem and are monitored using yellow, white or blue colored sticky cards. Figure 6 shows how small these insects are in comparison to a fungus gnat and coin. You may inherit a thrips problem when buying nursery grown plants. Thrips can transmit spotted wilt virus to several vegetable and ornamental plants (Powell and Lindquist, 1992). Therefore, beware!

There are a few predatory species on other small insects, mites and other thrips (Carr, 1979). Fortunately, thrips are a minor problem in the landscape, or at least most of the time.

Order: Homoptera (Aphids, Scales, Adelgids, Mealybugs, Psyllids, Whiteflies, Leaf Hoppers, and Cicadas)

All Homoptera insects are plant feeders and are the plant pest most often encountered by gardeners. Aphids, scales, mealybugs, adelgids, psyllids and whiteflies are the most recognizable pests infesting plants in this group.

Insects in the order Homptera exhibit physical differences. For example, most species have wings, but some are wingless and male scale insects have just one pair of wings. They come in a variety of sizes. Cicadas are some of the largest species in this order. Figure 12 shows an adult and nymph cicada together for size comparison.

Figure 12. Cicada adult and nymph.

Figure 12. Cicada adult and nymph.

Figure 13.

Figure 13. The cicada’s mouthparts are a good representation of homopteran mouthparts in general.

Members of this order also share a number of common characteristics. Their mouthparts are piercing-sucking and originate from the back of the head (Figure 13); however, some feed on plant leaves while others, like nymph stage cicada and some species of aphids feed on roots. Homopteran insects undergo simple metamorphosis: egg, nymph, adult. The nymph stage, in most cases, looks like the adult except it is smaller in size, has no wings, and cannot reproduce.One Homptera insect, the aphid, is very successful at reproducing. Most species of aphid can produce live young (Figure 14). Once a plant is infested, nymphs and adults feed on the same plant at the same time. This is why the control of homopteran pests is not to be ignored when the population is large on a single plant. Parthenogenesis occurs in many species (Borer et al, 1989).

Figure 14. Aphid giving birth to live young.

Figure 14. Aphid giving birth to live young.

Figure 15.

Figure 15.  Homopteran adults hold their wings roof-like, not flat, over thier bodies.

Homopteran adults have four wings which they hold roof-like over the body at rest. (See Figure 15.) Their mouth parts are called piercing-sucking due to the narrow stylets or needle-like structures, which form an effective tube for piercing plant cells and tissues for plant sap uptake. Homopteran mouthparts are very effective at transmitting some plant diseases, particularly viruses. This order is closely related to insects in the Hemiptera (Borer et al, 1989).

Figure 16.

Figure 16. Psyllid damage to boxwood.

Damage: Typical plant damage by Homoptera insects is to leaves. When leaves are fed upon by aphids, they become puckered and begin to yellow and are called chlorotic (e.g. chlorophyll destruction). Psyllids (shown in Figure 16) cause a leaf cupping effect on boxwood. The many scale insects that feed on stems and leaves can cause an increase in leaf yellowing and stunt the growth of the plant. Aphids, scales, whiteflies, and many leafhoppers produce a sugary excrement called ‘honey dew’ while feeding. The resulting honeydew is colonized by a mold that turns the sticky honeydew black and is commonly referred to as sooty mold. (See Figure 17.) The presence of sooty mold on leaves, bark and objects in close proximity to the infested tree or group of plants is a telltale sign of these homopteran insects. Another telltale sign of honeydew-sooty mold combination or just the honeydew is the sudden appearance of ants and yellow jackets which feed on the sugary substance.

Figure 17. Sooty mold.

Figure 17. Sooty mold.

Figure 18.

Figure 18. Witch-hazel leaf gall.

A few aphids can make galls. Figure 18 shows the witch-hazel leaf gall aphid (Hormaphis hammamelidis) that makes a conical-shaped gall on the upper leaf surface of witch-hazel. There are several aphid species that feed on stems of herbaceous garden plants, but cause little damage. Figure 19 shows yellow stem aphids on milkweed.

Figure 19.

Figure 19. Yellow stem aphids.

Spittlebugs, sometimes called froghoppers (Cercopidae) feed on an array of trees, shrubs, and grasses. The nymphs produce white, bubbly froth or spittle over their bodies (Borer et al, 1989). When you see honey dew and spittle mass, think Homoptera.

Prolonged homopteran feeding causes extensive plant leaf curling, puckering, yellowing, premature leaf drop, and stunted growth of the entire plant at high pest populations. If not controlled, pests in this order can cause severe plant damage. Populations can increase quickly. Insects are visible to the naked eye and congregate in groups on buds, leaves, and stems depending on the host plant species. For example, the hemlock woolly adelgid (Adelges tsugae) shown in Figure 20 colonizes branch tips (young growth) at the needle base, inserting its piercing-sucking mouthparts into the stems for sap uptake. A serious pest of eastern hemlock (Tsuga Canadensis), without adequate control measures woolly adelgid can build up quickly causing leaf (needle) yellowing, browning, premature leaf drop, and eventual death of the tree.

Figure 20. Hemlock Wooly Adelgid.

Figure 20. Hemlock Woolly Adelgid white egg masses.

fig-21-ela-fact-sheet-12-homoptera-scale-on-hawthorn-bw

Figure 21. Homoptera scale on hawthorn.

There are many scale species that infest woody and herbaceous plants. Figure 21 shows scale on a hawthorn tree. This scale appears as an oval-shaped bump. Euonymus scale is common in the landscape and causes leaf yellowing and stunted growth. Figure 22 shows this white colored scale on euonymus leaves.

Figure 22.

Figure 22. Scale on euonymus.

Figure 16 shows the leaf cupping distortion caused by the boxwood psyllid (Psylla buxi). This small, gray-colored nymph attacks the succulent, young growth. The green adult has clear wings and is rarely seen.

I have seen extensive needle yellowing on Taxus (yew) due to the taxus mealybug (Dysmicoccus wistariae) which likes the protection of dense foliage, which provides shade and higher humidity for these white colored soft bodied insects. Harvestmen or daddy-longlegs “spiders” appear in greater numbers in yews with taxus mealybug infestations. Harvestmen are predatory and possibly feed on this pest. Harvestmen also feed on some scale insects.

There are several insect predators that feed on aphids and mealybugs. One is the “bee mimic” or hover fly (Diptera: Syrphidae) which is commonly seen in flower beds. This dipteran larvae attacks aphids, but the adult fly feeds on nectar (Borer et al, 1989: Carr, 1979). Mealybugs, aphids, and scales are preyed upon by ladybugs (Coleoptera: Coccinellidae) and lacewing larvae (Neuroptera: Chrysopidae and Hemerobiidae) (Borer et al, 1989: Carr, 1979). A few other predators also attack homopteran pests.

Figure 23.

Figure 23. True bugs hold their wings flat over the body at rest.

Order: Hemiptera (The True Bugs)

Insects in this order are called the true bugs and have four wings held flat over the body at rest as shown in Figure 23. Figure 24 illustrates some common representatives that you may recognize from your gardening endeavors.  The front wings have a basal portion that is thick and leathery and an apical (tip) portion that is membranous. The hind wings are entirely membranous. Some species are wingless. The mouthparts are piercing-sucking type, segmented, and attached at the front of the head. Metamorphosis is simple with most having five nymphal instars (Borer et al, 1989; Carr, 1979). Refer back to Figure 2.

Figure 24.

Figure 24. Common Hemiptera. Some are garden pests, some are not pests, and a few are aquatic.

Several hemipterans are plant pests that feed on plant leaf sap. Leaf damage is evident as a flecking or stippling causing light or dark spots depending on the host plant (Figure 25). Continued feeding leads to a dulling of leaf tissue called bronzing. Touching infested plants will cause plant bugs to scatter by quickly jumping or flying.

Figure 25.

Figure 25. Hemipterans feed on plant leaf sap causing light-colored flecking. Shown here is damage to cherry.

Some recognizable pests in this order are the chinch bug (Blissus leucopterus), a common lawn pest that feeds on grass blades, and the rhododendron lace bug (Stephanitis rhododendri) that feeds on rhododendron leaves.

Rhododendron, azalea, and andromeda lace bugs are also common in the landscape. The adults have a wing morphology that resembles lace fabric. See Figure 26.  Feeding damage first appears as dots (feeding spots) on the undersides of leaves, and continued feeding by these insects leads to yellowing leaves. As feeding populations build up, leaf damage becomes more severe causing leaves to show surface spots that turn pale white or yellow, with some plant species showing leaf curling and leaf drop.

Figure 26.

Figure 26. Lace bugs get their name from their wing morphology.

Other garden pest hemipterans are the fourlined plant bug (Poecilocapsus lineatus) that feeds on mint, currant and gooseberry and the tarnished plant bug (Lygus lineolaris) that feeds on many fruits and vegetable crops, as well as on China aster (Callistephus), dahlia, gladiolus, impatiens, salvia, viburnum, and zinnia to name a few targets(Carr, 1979; Pirone, 1978).

The hemipteran western conifer seed bug (Leptoglossus occidentalis) is a frequent home invader in autumn and regarded as a nuisance pest. It is attracted to heat on cool autumn days particularly on white houses.

Some hemipterans are beneficial garden insects. There are several species of assassin bugs (Reduviidae), which feed on a variety of garden pests. The minute pirate bug (Orius sp.) feeds on aphids, thrips and spider mites (Carr, 1979). Figure 27 shows this predator feeding on a thrips.

Figure 27.

Figure 27. A adult pirate bug feeds on a thrips.

Order: Diptera (True Flies)

Insects in this order have one pair of wings. Whereas other insects have hind wings, Diptera species have knob- like structures called halteres that function as balancing organs. Halteres allow flies to maneuver very quickly in flight making them almost impossible to catch. Adult mouthparts vary by species and can be either sucking, sponging, piercing, or lapping. Mouthparts of larvae are hook-like or chewing. Larvae are generally called maggots and are white, legless, and worm-like. Diptera undergo complete metamorphosis. Refer back to Figure 2 (Borer et al, 1989; Pirone, 1978).

The common dipteran plant pests feed as larvae on plant tissues in gardens and orchards. Some are leaf miners and are considered an aesthetic pest. Others such as stem, fruit and root borers are more serious. A few cause galls.

The apple maggot (Rhagoletis pomonella) feeds on apple, plum, cherry, and blueberry and can be economically damaging to these crops. The larvae bore into the fruits causing them to be distorted or undersized, or to develop fungal or bacterial decay problems (Carr, 1979; Borer et al, 1989).

Leafminers (Liriomyza spp.) make feeding tunnels or mines between the upper and lower leaf surfaces of many woody, herbaceous garden plants and vegetable crops. Damage rarely kills the plant. Leaf miners are considered an aesthetic pest to people who find their serpentine mines unsightly. I like the way they look.

Holly leaf miner (Phytomyza ilicis) and the native leaf miner (P. ilicicola) attack Ilex (holly) and make blotches and serpentine mines on leaves (see Figure 28). Adult females deposit eggs in the lower leaf surfaces (Pirone, 1978). Leaf drop can occur when blotches are large on individual leaves.

Figure 28. Holly leaf miner damage.

Figure 28. Holly leaf miner damage.

There are some fly pests of economic importance in farming, such as the onion maggot (Hylemya antiqua) and pepper maggot (Zonosemata electa) (Carr, 1979).

There are several dipteran beneficials that are predatory on homopteran pests such as aphids, mealybugs, and other soft bodied insects. The most obvious to gardeners is the hover fly (Syrphidae), sometimes called “bee mimics” because of their black and yellow abdominal markings (shown in Figure 29). Hover fly larvae are predatory, but the adults feed on nectar. Many hover fly maggots hide on leaves and twigs to feed on aphids.

Figure 29. Adult hover fly.

Figure 29. Adult hover fly.

Robber flies (Figure 30) are another important predatory group in the Diptera order. Robber flies (Asilidae) are robust, fast moving flies that prey on many insects. Adults fly and attack very quickly. They are known to feed on other flying insects such as leafhoppers, butterflies, true bugs, and beetles. Larval robber flies have been observed attacking white grubs (Coleoptera) in soil and grasshopper (Orthoptera) eggs (Carr, 1979; Borer et al, 1989).

Figure 30. Robber fly.

Figure 30. Robber fly.

The most well-known dipteran predatory group is flies in the family, Tachinidae. Tachinid flies feed as larvae on other insects particularly, caterpillars, sawflies, true bugs, beetles, and grasshoppers (Carr, 1979; Borer et al, 1989). Notably, the tachinid Istocheta aldrichi attacks the Japanese beetle adult. This fly (adult parasitoid) attaches one egg about 1mm in diameter to the thorax of an adult beetle and within 24 hours, the egg hatches. The maggot that is released into the beetle’s body  devours the internal organs, slowly killing the beetle (Vittum et al, 1999). In July and August you may see this white egg on an adult Japanese beetle thorax. Tachinid flies are important in natural biological control.

Order: Lepidoptera (Butterflies and Moths)

This is the order that most insect novices are familiar with. Insects in this order have complete metamorphosis. (Refer to Figure 31). Additionally, the larvae and adults have different feeding hosts, habits, and mouthparts. Larvae are mostly leaf chewers, and some are leaf miners, gall makers, and borers into herbaceous stems, fruits, and wood (Borer et al, 1989). The mouthparts of the larvae (caterpillars) are the chewing type. Caterpillars can be found feeding on a huge variety of plants. On the other hand, the mouthparts of the adults are modified tube-like structures for sucking up plant juices/compounds (e.g. nectar). Adult butterflies and moths are not the leaf chewers and feeders, their larvae (caterpillars) are (Borer et al, 1989).

Figure 31.

Figure 31. A. Coleoptera; B. Lepidoptera.

The larvae in this order are capable of producing silk. According to Borer, et al (1989), the larval silk glands are modified salivary glands which many species use to tie and roll leaves together, construct silken structures of various types to feed and for protection (e.g. tent caterpillars and webworms).

Damage: Plant damage is common to leaves being fed upon by the larvae. Common lepidopteran garden and landscape pests are the winter moth (Operophtera brumata), gypsy moth (Lymantria dispar), eastern tent caterpillar (Malacosoma americanum), forest tent caterpillar (M. disstria), fall webworm (Hyphantria cunea), and tomato hornworm (Manduca quinquemaculata).  There are also lepidopteran leaf miners, such as the white oak leaf miner, shown in Figure 32.

Figure 32

Figure 32. White oak leaf miner.

In general, lepidopteran larvae consume leaves differently depending on their size (age). For example, larger (later instar) caterpillars will feed on leaf edges and work their way towards the center of the leaf without consuming many major leaf veins. Smaller (young or early instar) larvae will make holes in the leaf, and as they increase in size they will start consuming leaf edges as shown in Figure 33.

Figure 33.

Figure 33. Leaf damage from lepidopteran larvae includes holes as well as ragged leaf edges.

The leaf damage caused by the winter moth demonstrates this feeding behavior. Winter moth larvae enter leaf buds of trees (maples, oaks, ash, etc) and feed on the tightly packed buds. As the leaf buds unfurl, the growing larvae continue to feed and begin consuming the leaf edges, moving closer to the leaf center to consume most, if not all, of the leaves.

Without careful inspection, leaf damage caused by some adult beetles (Coleoptera) can be confused with leaf damage caused by caterpillars (Lepidoptera).

Many species of butterflies are important pollinators of perennial and annual garden plants.

Order: Coleoptera (Beetles)

Insects in this order are known as beetles and are very recognizable to the gardener. Adult beetles have four wings, but the front wings are called elytra and serve as protective sheaths or coverings for the membranous hind wings, which are used for flying. Mouthparts are chewing. For snout beetles (weevils) the mouthparts are constructed into a long snout with the chewing apparatus located on the end. Beetles undergo complete metamorphosis. Refer back to Figure 31.

Many beetles feed on trees, shrubs, and herbaceous plants including turfgrass roots. In several situations, the adults and larvae can be pests. The Japanese beetle (Figure 34) is a good example. It feeds on the roots of many plants, particularly the roots of turfgrasses, and the adults feed on close to 300 species of plants that include ornamental trees, shrubs, vegetables, vines, flowers, and weeds (Vittum et al, 1999).

Figure 34. Japanese beetles.

Figure 34. Japanese beetle adults cause leaf skeletonization while feeding.

On the other hand, beetles in the family Cerambycidae (longhorn beetles) are wood borers in the larval stage, but the adults rarely feed to the point of being considered pests of desirable garden and landscape plants.

The Asian longhorn beetle (Anoplophora glabripennis) an introduced pest from Asia, is the most recognizable cerambycid pest to hardwood trees in the Northeast of recent years. It is a very destructive larval wood borer, but the adult does not feed to pest status.

There are thousands of species of beetles and they range from plant feeders to decomposers. Some are predators, others are fungal feeders, and a few are parasitic (Borer et al (1989).

Figure 35.

Figure 35. Flea beetle damage on plantain.

Beetle adults will chew leaves; the larvae feed on roots and bore into herbaceous stems and wood. Beetles in the family Chrysomelidae (a large family of leaf chewers) are called leaf beetles. Well-known beetles in this family are the Colorado potato beetle (Leptinotarsa decemlineata) and the lily leaf beetle (Lilioceris lilii). Most beetles in the Chrysomelidae family have a feeding behavior similar to the Homoptera and Hemiptera, in that the chrysomelid larvae feed on the same host as the adults. What is different is that many chrysomelid larvae are leaf skeletonizers, whereas the adults make holes in the leaves. The combination of skeletonization and holes in leaves is evident with many leaf beetles including the viburnum leaf beetle (Pyrrhalta viburni) and the imported willow leaf beetle (Plagiodera versicolor) (Cranshaw, 2004). Characteristic beetle leaf damage is generally holes in the leaves (Figure 35). An exception is the black vine weevil (Otiorhynchus sulcatus), which feeds at night on the edges of rhododendron and yew leaves and makes the characteristic leaf notch shown Figure 36.

Figure 36.

Figure 36. Leaf notches from black vine weevil (Otiorhynchus sulcatus).

Damage to leaves by small caterpillars, snails, and slugs can be confused with beetle damage (Figure 37). This easy confusion demonstrates the importance of a gardener properly identifying the host plant and properly investigating the type of damage. See the resources list below for good books on insect identification specific to garden plant species.

Figure 37.

Figure 37. Leaf damage from caterpillars, snails, or slugs may be confused with beetle damage. Illustrated here is a hosta leaf with slug damage.

To summarize, common beetle damage to leaves includes partial leaf consumption leaving behind main leaf veins, leaf holes of various sizes, leaf skeletonizing (both leaf surfaces are removed, leaving the veins exposed), and window pane damage (one leaf surface is fed upon leaving the other surface intact allowing light penetration).

Order: Hymenoptera (Bees, Ants, Wasps, Sawflies, and Parasitic Wasps)

This order includes many beneficial insects, most of which are in the class Hexapoda. Insects in this order generally have four membranous wings and the hind wings are smaller than the front wings; however, some species are wingless. The mouthparts are mandibulate (chewing), yet some species have modified mouthparts for liquid uptake (bees). Metamorphosis is complete. Larvae are maggot-like or grub-like (Borer et al, 1989).

The Hymenoptera comprise insects that display social organization (i.e. colonies) such as honey bees, hornets, yellowjackets, and ants to name a few. There are several species in this large order that do not live in a group or colony, but are solitary. Solitary species include the parasitic wasps and bees that prey on other insects, leafcutting bees, some digger bees, and stem sawflies. (Borer et al, 1989).

Several solitary species that are very important in natural biological control as parasites on other insects include species in the following families: Braconidae, Ichneumonidae, Mymaridae, Eulophidae, Encyrtidae, Chalcididae, and a few other families. Many species are egg or larval parasites of insects, spiders, and spider egg sacs (Borer et al, 1989).

Major plant pests in the Hymenoptera are the sawflies. Sawfly larvae feed on both deciduous and evergreen trees and shrubs. Larvae are fleshy, mostly non-hairy and caterpillar-like. There are several plant feeding families of sawfly. Depending on the family, certain species feed on broadleaved and needle foliage, cones, catkins, stems, fruits, and wood. A few are gall makers and leaf miners (Figure 38). Not all sawflies are pests that cause economic damage to plants (Borer et al, 1989).

Figure 38. Cup gall on white oak.

Figure 38. Cup gall on White Oak.

The birch leaf miner (Fenusa pusilla) is a sawfly that makes brownish colored blotches in birch leaves (Borer et al, 1989). The elm leaf miner (F. ulmi) can be found mining and causing severe damage to elm leaves (Borer et al, 1989). Figure 39 shows sawfly damage on oak.

Figure 39. Sawfly damage on Black Oak.

Figure 39. Sawfly damage on Black Oak.

Most sawflies encountered by the gardener and arborist will be in the family Tenthredinidae (common sawflies). The common roseslug (Endelomyia aethiops) (Figure 40) is in this family, and the larvae feed on the undersides of rose leaves causing leaf skeletonizing or window pane damage (Cranshaw, 2004).

Figure 40.

Figure 40. Common roseslug.

Pine trees are attacked by the European pine sawfly (Neodiprion sertifer). The larvae feed in groups and have black heads and a light green body. Figure 41 shows a Midwestern species called the redheaded pine sawfly (Neodiprion lecontei). It also feeds on pines.

Figure 41. Redheaded pine sawfly on

Figure 41. Typical pine sawfly damage is chewed needles that result in reduced needle length.

Although important pollinators, leaf cutter bees (Megachilidae: Megachile spp.) remove portions of leaves on many plants including roses, Virginia creeper, lilac, and ash (Cranshaw, 2004). They use the leaf portions to construct nest cells (Cranshaw, 2004).

The Hymenoptera include some very important pollinators such as honey bees (Apis spp.), bumblebees (Bombus spp.), and several wasp species.

Plant Damage and Associated Insect Order

The feeding habits of insects reveal which group they are in. The following summary of plant damage will help you narrow down or discern the pest you are interested in managing. It helps considerably if you properly identify the plant in question before you begin your investigation of the specific pest.

  • Leaves that display distortion, puckering and/or curling; yellowing of leaves with accompanying honey dew = Homoptera.
  • Spittle on stems of field and meadow plants (some woody plants) = Homoptera
  • Leaves that display distortion with no honey dew = Thysanoptera.
  • Leaf stippling or spotting. Stipple spots are small, whitish or light colored, sometimes dark colored = Hemiptera and Homoptera; possibly Thysanoptera.
  • Leaf cutting (semicircular), and notching = Hymenoptera and Coleoptera.
  • Leaf holes = Coleoptera, Lepidoptera, and the non-insect group of slugs and snails.
  • Leaf miners that cause serpentine mines and/or blotches = Diptera, Hymenoptera, and Lepidoptera.
  • Leaf skeletonizing (veins exposed) or window pane (only one leaf surface has been removed by feeding) = Coleoptera and Hymenoptera.
  • Leaves tied or rolled with silken threads = Lepidoptera.
  • Pine needles reduced in size = Hymenoptera.

When you observe the signs of specific plant damage, you can better select the possible pest or pests from the insect orders listed above. Most garden plant damage done by insects will fall into these insect orders. Good luck with your plant pest diagnosis.

Print and Internet Resources

Books

Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An Introduction to the study of Insects. 6th ed. Saunders College Publishing, Harcourt Brace College Publishers, New York. 875p. Note: this is the standard college entomology textbook of insect taxonomy and biology; many editions with the first in 1954.

Cranshaw, W. 2004. The ultimate guide to backyard bugs. Garden Insects of North America. Princeton University Press, Princeton, New Jersey. 656p. Note: This is a great book covering all major garden and landscape insect and mite pests. Color photographs. An appendix on host plant genera and associated insect and mite pests is included.

Davidson, J. A. and M. J. Raupp. 2010. Managing Insects and Mites on Woody Plants: an IPM Approach. Second Edition. Tree Care Industry Association, Londonderry, New Hampshire. 165p. Note: This book gives an Integrated Pest Management (IPM) approach to insect pest control on woody plants. It reviews IPM practices and techniques, biological control organisms, monitoring for insect pests by month and host plants, plant damage symptoms and control strategies. Color photos and black and white illustrations.

Deardorff, D and K. Wadsworth. 2009. What’s wrong with my Plant? (And how do I fix it?): A visual guide to easy diagnosis and organic remedies. Timber Press, Portland, Oregon. 451p. Note: This book is very user friendly with color drawings and color photos. You can diagnose a plant problem easy and accurately.

Hartman, J. R., T. P. Pirone and M. A. Sall. 2000. Pirone’s Tree Maintenance. 7th ed. Oxford University Press, Inc., New York. 545p. Note: this book is best used to narrow down the pest you don’t know that is on a tree that you do know. Insects and diseases.

Johnson, W. T. and H. H. Lyon. 1991. Insects That Feed On Trees And Shrubs. 2nd ed (revised). Cornell University Press, Ithaca, N.Y. 560p. Note: this book is the most widely used in tree and shrub pest control. Gives the biology of insect pests and associated tree and shrub host plants. Color photos.

Powell, C. C. and R. K. Lindquist. 1992. Ball Pest & Disease Manual. Disease, insect and mite control on flower and foliage crops. Ball Publishing, Geneva, Illinois. 332p.

Pirone, P. P. 1978. Diseases & Pests of Ornamental Plants. 5th ed. John Wiley & Sons, New York. 566p. Note: this book is best used to narrow down the pest you don’t know that is on a plant that you do know.

Vittum, P. J., M. G. Villani and H. Tashiro. 1999. Turfgrass Insects of the United States and Canada. 2nd ed. Cornell University Press, Ithaca, New York. 422p. Note: the most comprehensive text on insect and mite pests infesting turf. Color photos.

References on Pollinators

Holm, H. 2014. Pollinators of Native Plants. Pollinator Press LLC, Minnetonka, Minnesota. 305p. Note: excellent color text on all of the major plant pollinators.

Shepherd, M., S. L. Buchmann, M. Vaughan, and S. H. Black. 2003. Pollinator Conservation Handbook. The Xerces Society, Portland, Oregon. 145p. www.xerces.org.

Internet Resources

The following websites are standard and trustworthy institutions for insect pest and plant disease information.

University of Massachusetts Cooperative Extension, www.UMassGreenInfo.org. Sign up for the free landscape message to keep current about the major landscape pests.

University of New Hampshire Cooperative Extension, http://www.extension.unh.edu/

University of Maine Cooperative Extension, http://www.extension.umaine.edu/

University of Vermont Cooperative Extension, http://www.uvm.edu/extension/

University of Connecticut Cooperative Extension, http://www.extension.uconn.edu/

The most comprehensive website about all invasive organisms in the United States is www.invasive.org. This website does not give control measures, but shows in photographs what the insects look like. The site covers all types of pests: insects and insect relatives, invasive plants, and plant disease organisms.

Literature Cited

Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An Introduction to the study of Insects. 6th ed. Saunders College Publishing, Harcourt Brace College Publishers, New York. 875p.

Carr, Anna. 1979. Rodale’s Color Handbook of Garden Insects. Rodale Press, Emmaus, Pennsylvania. 241p.

Cranshaw, W. 2004. The ultimate guide to backyard bugs. Garden Insects of North America. Princeton University Press, Princeton, New Jersey. 656p.

Pirone, P. P. 1978. Diseases & Pests of Ornamental Plants. 5th ed. John Wiley & Sons, New York. 566p.

Powell, C. C. and R. K. Lindquist. 1992. Ball Pest & Disease Manual. Disease, insect and mite control on flower and foliage crops. Ball Publishing, Geneva, Illinois. 332p.

Vittum, P. J., M. G. Villani and H. Tashiro. 1999. Turfgrass Insects of the United States and Canada. 2nd ed. Cornell University Press, Ithaca, New York. 422p.

About the Author

Bruce Wenning is a horticulturist at The Country Club in Brookline, MA. He has university degrees in plant pathology and entomology. He has been on the ELA Board since 2003. Bruce worked for turfgrass entomology professor, Dr. Patricia Vittum in the 1980s at The UMass Suburban Experiment Station, Waltham. Bruce also taught and teaches about landscape insect pests for Arlington Community Education and local garden clubs.

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