A Guide to Insect and Mite Pests of Plants for Master ...



A Guide to Insect and Mite Pests of Plants for Master Gardeners

Frank A. Hale: Professor Entomology and Plant Pathology

David L. Cook: Davidson County Extension Agent

Slide 1- Introduction: In your Master Gardener notebook there are three chapters on insects: Applied Entomology, Insect and Mite Pests of Ornamental Plants, and Insect and Mite Pests of Vegetables and Fruits. The Applied Entomology chapter deals with types of insect injury, insect reproduction, growth and development, control of insects with insecticides and even the benefits and value of insects. The chapter on Insect and Mite Pests of Ornamental Plants discusses key plants and key pests, early pest detection, pest control decision-making, integrated pest management (IPM), chemical control, oils, soaps, monitoring, and examples of the most common ornamental insect and mite pests. The chapter on Insect and Mite Pests of Vegetables and Fruit discusses steps in managing pests, pesticide safety, and examples of the most common insect and mite pests of vegetables and fruit. This program will present some of the most common insect and mite pests of ornamental plants in Tennessee. Pesticide recommendations will be limited and directed to only a few groups of insect or mite pests. For current listings of insecticides and control measures refer to University of Tennessee Extension fact sheets and publications found on UT’s web site:

Slide 2 – Interesting Insect Facts: Fossils indicate insects have been around for 350 million years. There have been over 1 million insects identified with many more yet to be discovered. Insects thrive in more environments than any other group of animals. They eat the choicest foods on man’s table and can eat the table too.

Slide 3 – Species: Insects are so abundant that actually 1 in 5 living animals species is a beetle. Insects are organized into large groups called “Orders”, and within each insect order are thousands of species.

Slide 4 – Growth and Development - Gradual Metamorphosis: The series of form changes as an insect develops from egg to adult is called metamorphosis. Some insects develop through three gradual steps: (1) egg, (advance slide) (2) nymph, (advance slide) and (3) adult. The immature insects are called nymphs, which resemble the adults. Examples of gradual metamorphosis include aphids, grasshoppers, squash bugs, leafhoppers, and plant bugs.

Slide 5 – Growth and Development – Complete Metamorphosis: Complete metamorphosis involves four steps: (1) egg, (2) larva, (3) pupa, and (4) adult. The immature stage is called a larva, which does not resemble the adult insect. The pupa stage (advance slide) is a resting stage, but inside the pupal skin drastic changes are taking place. A fully formed adult with wings will emerge out of the pupa stage. The larvae and adults of these insects may live on different foods, have different mouthparts, and many other differences. Examples of complete metamorphosis include beetles, butterflies and moths, and flies.

Slide 6 – Ways in Which Insects Injure Plants: Probably 95% of insect injury to plants is caused by feeding. (advance slide) Insects that injure plants through their feeding activity may chew off external parts of plants, (advance slide) suck sap from cells, (advance slide) or feed within plant tissues. Internal injury may result in the formation of galls (advance slide). Gall insects sting plants and cause them to produce a structure of deformed tissue. Although the gall is entirely plant tissue, it is the insect that controls and directs the form and shape of the growing gall. (advance slide) Sometimes plant injury is easily unnoticed because subterranean insects cause the damage. (advance slide) Insects may also damage plants by laying eggs in critical plant tissues. (advance slide) Insects may cause more serious injury to plants by the spread of disease organisms. Insects vector over 200 plant diseases.

Slide 7 – Types of Injury – From Chewing Insects: This is the most common type of injury caused by insects. Notching of leaf margins is characteristic of many insects, such as beetles and caterpillars. (Advance slides, 4 clicks) Leaves can sustain considerable chewing injury and still function somewhat normally.

Slide 8 – Types of Injury – From Sucking Insects: Some plant pests have beak-type mouthparts and are only able to remove plant liquids. This type of injury may result in localized areas of dead cells, whitish or yellowish spots known as stippling, or yellowing of leaf tissue known as chlorosis. (Advance slides, 4 clicks) Plant bugs, scale insects, and mites can cause this type of injury.

Slide 9 – Types of Injury – From Internal Feeders: Many insects feed within plant tissues during part or all of their destructive stages. (Advance slides, 4 clicks) Borers and leaf miners are examples of these plant pests. Nearly all of the internal feeding insects live inside the plant during only part of their lives, and emerge usually as adults.

Slide 10 – Types of Injury – From Internal Feeders: Some insects and mites through their egg laying and feeding activity induce plants to produce abnormal growths called galls. Most galls do not damage plants except for disfiguring the plant parts. (Advance slides, four clicks) Certain species of mites and small non-stinging wasps are responsible for many plant galls.

Slide 11 – Types of Injury – From Subterranean Insects: These types of pests differ from above-ground pests only in their position with reference to the soil surface. Some subterranean insects spend their entire life cycle below ground; others will have one life stage that is spent above ground. (Advance slides, 3 clicks) White grubs and wireworms are common subterranean insects. White grubs are the larvae of scarab beetles; wireworms are the larvae of click beetles.

Slide 12 – Types of Injury – From Egg Laying: Insects may damage plants by laying eggs in critical plant tissues. If injury is severe the entire twig may die. (Advance slides, 4 clicks) Cicadas and tree crickets are examples of these types of insects.

Slide 13 – Types of Injury – Insects as Vectors of Diseases: More than 200 plant diseases are spread by insects. These include viral, fungal, and bacterial diseases.

Slide 14 – Types of Injury – Insects That Spread Viral Diseases: Viral diseases are generally spread by insects with beak-type sucking mouthparts. The virus is introduced in the insect’s saliva during feeding. (Advance slides, 2 clicks) Aphids are known vectors many viral diseases including tomato mosaic virus.

Slide 15 – Types of Injury – Insects That Spread Fungal Diseases: Some insects carry fungal spores on their bodies from one plant to a susceptible surface of another plant. (Advance Slides, 2 clicks) The native elm bark beetle is a primary insect in the transmission of Dutch elm disease.

Slide 16 – Types of Injury – Insects That Spread Bacterial Diseases: Bacterial diseases can also be spread through insect feeding. Leafhoppers are insects with beak-type sucking mouthparts that transmit bacteria in their salvia. (Advance slides, 3 clicks) Bacterial leaf scorch, a disease that attacks pin oaks, is vectored by certain species of leafhoppers. This is a serious disease of pin oaks that results in the death of large trees.

Slide 17 – Types of Injury – Pollinators That Spread Diseases: Sometimes beneficial insects such as bees spread diseases. (Advance slides, 2 clicks) Bees pollinating the flowers can spread a common disease of apple, pear, and ornamental pear trees called fire blight.

Slide 18 – Insect Pests with Chewing Mouthparts: The next series of slides will give examples of some of the most common insect pests with chewing mouthparts.

Slide 19 – Bagworm: Bagworm caterpillars feed on over 128 species of deciduous and evergreen woody ornamentals. In late summer the maturing caterpillars finish feeding and firmly attach their silken bags to the twigs and pupate.

Slide 20 –Comparing Eastern Tent and Forest Tent Caterpillars: Tent caterpillars are among the earliest springtime defoliators of deciduous trees. Both species emerge in the spring from egg masses laid on twigs of the host tree. The eastern tent caterpillar can be identified by the white stripe down its back. The forest tent caterpillar has a series of keyhole-shaped spots down its back. Both species have only one generation per year.

Eastern tent caterpillars construct their silken nest at a major branch fork or crotch on the host tree.

Slide 21 – Fall Webworm: The fall webworm feeds on almost all shade, fruit, and ornamental trees, except conifers. There are two color variations of this caterpillar, one blackheaded and the other redheaded. Unlike tent caterpillars, their silken webs are out on the ends of branches. Feeding occurs only on the foliage that is inside the web. The fall webworm has three generations per year in Tennessee. Sometimes the entire host tree will be covered in silk.

Slide 22 – Cankerworms: Both spring and fall cankerworms hatch from eggs in the spring and feed on the same host plants. The common names of these caterpillars indicate the respective seasons during which their eggs are laid. To lay eggs on the host tree the wingless, adult, female moth has to climb up the truck. Cankerworms devour all but the midrib of the leaf and often defoliate entire trees. After four to five weeks of feeding, the mature caterpillars spin down from the trees, enter the soil, and pupate in a cocoon.

Slide 23 – Yellownecked Caterpillar: Hatching from clusters of eggs laid on the underside of leaves, young yellownecked caterpillars chew off outer leaf areas, but as they begin to grow they will consume the entire leaf. The caterpillar gets its name from the bright orange-yellow segments behind its head. Fully-grown caterpillars crawl down the truck and burrow into the soil to pupate.

Slide 24 – Orangestriped Oakworm: The orangestriped oakworm can be identified by its five orange stripes and a pair of horn-like structures near its head. The horns are sometimes mistaken for antennae. Young caterpillars feed on entire leaves except for the veins. Older caterpillars eat all but the main leaf vein as they defoliate one branch before going on to another. Mature caterpillars crawl away from trees and pupate in the soil.

Slide 25 – Sawflies: Sawflies may look like caterpillars, but they are actually the larvae of small non-stinging wasps. The female has a saw-like ovipositor, which is used for sawing slits in plant material in which she lays her eggs.

Slide 26 – Sawflies: Sawfly larvae have more than five pairs of prolegs, generally eight. Caterpillars have two to five pairs of prolegs. It is important to know the difference because Bt products that control caterpillars will not work on sawflies. The introduced pine sawfly originally from Europe, is a common pest of white pine and other pines.

Slide 27 – Conifer Sawfly Feeding Injury: Sawflies in the first larval stages eat only the outer portions of the needles; later the entire needle may be consumed. There are more than three dozen species of conifer sawflies.

Slide 28 – Scarab Beetles: There are many species of scarab beetles; some are more commonly recognized than others. The May and June beetles can be identified by their brown or black colors. May and June beetles are mainly nocturnal, feeding only at night on deciduous trees and shrubs. During the day they hide under litter or in the soil.

Japanese beetles are metallic green with bronze wing covers. Japanese beetle feeding injury creates a lacelike appearance to foliage called skeletonizing. The adult beetles feed during the day on nearly 300 plant species. The larvae of scarab beetles are called white grubs and are major pests of turf grasses. The green June beetle is one of the larger species. Its wing covers are green with brown margins.

Slide 29 – Leaf Beetles: The leaf beetle family contains around 1,500 species. Both larval and adult stages are plant feeders with larvae skeletonizing the underside of leaves, and adults chewing holes in leaves. The adult beetles range in size from 1/10 to nearly ½ inch in length and most are somewhat oval in shape. Some species are brightly colored; others may have spots, stripes, or unusual markings.

Slide 30 – Insect and Mite Pests with Sucking Mouthparts: The next series of slides will give examples of some of the most common insect pests with sucking mouthparts.

Slide 31 – Aphids: Virtually every plant has at least one aphid species that attacks it. Aphids have complicated life cycles that involve winged and non-winged forms, sexual and asexual reproduction, and primary and secondary host plants. The large photo shows a female aphid giving live birth. Besides the injury their feeding may cause, aphids also excrete large amounts of liquid waste called honeydew, upon which a black fungus called sooty mold grows. Oils and insecticidal soaps will help to control aphid problems.

Slide 32 – Sooty Mold: Sooty mold is a fungus that appears as a black coating on the surface of leaves, twigs, and branches. It is not pathogenic, but obtains its nourishment from insect honeydew. The presence of sooty mold indicates an insect infestation.

Slide 33 – Asian Woolly Hackberry Aphid: Some species of aphids have wax glands and are able to cover themselves with white, waxy threads giving them a woolly appearance. One such species, the Asian woolly hackberry aphid was first reported in Tennessee in 2001. This aphid completes its entire life cycle on hackberry trees. No serious injury is caused to the trees, but the excessive honeydew produced by the aphids may result in entire trees being covered with sooty mold. Large numbers of the multicolored Asian lady beetle may also be found on aphid-infested hackberry trees. Both the larval and adult lady beetles feed on aphids.

Slide 34 – Lace Bugs: Lace bugs, due to their small size are rarely observed, but their feeding injury rarely goes unnoticed. Feeding occurs on the underside of leaves, but the damage is always apparent on the upper leaf surface. Feeding injury results in white or yellowish spotting with severe injury producing bleached leaves. Another sign of lace bug feeding is the tiny dark spots of lacquer-like fecal material deposited on the underside of leaves.

Slide 35 – Euonymus Scale: Scale insects are divided into two types, armored and soft scale. Both types secrete a waxy cover, but only the cover of armored scales can be removed to reveal the scale insect beneath. Euonymus scale is an example of an armored scale. Females are oystershell shaped and brown in color; males are elongate and white in color. The orange colored nymphs are very small and are commonly called crawlers. Feeding injury causes yellowish spots on leaves, with heavily infested leaves dropping prematurely and branch dieback. Dormant oil and horticultural oil will help to control scale problems.

Slide 36 – Obscure Scale: Obscure scale is another example of an armored scale, which is mainly a pest of trees. This pest commonly attacks pin oaks. Obscure scales tend to settle close together; this results in layers of scales as they grow and enlarge. Severe infestations can result in major limb dieback of large trees.

Slide 37 – Tuliptree Scale: Tuliptree scale is an example of a soft scale. The waxy covering of soft scales cannot be removed; the cover is firmly attached to the body of the insect. Unlike armored scale insects, soft scale produce an abundance of honeydew, on which sooty mold may grow. Another major difference between the two types of scale is in their feeding habits. Soft scale feed on phloem sap whereas armored scale feed directly on plant cells. Systemic insecticides provide excellent control of soft scale.

Slide 38 – Mites: Mites are not true insects, but are related to spiders and ticks. Mites have tiny mouthparts modified for piercing individual plant cells and removing the contents. Oils and insecticidal soaps will help to control mite problems.

Slide 39 – Spruce Spider Mites: The spruce spider mite is a cool-season pest of needle-leaf evergreen plants such as arborvitae, false cypress, hemlock, juniper, pine, spruce, and others. These mites are active in the spring and fall. Feeding injury causes light-colored flecks on foliage, with infested trees displaying a yellowish or grayish appearance. Heavy feeding injury may result in premature needle drop.

Slide 40 – Southern Red Mite: The southern red mite is another cool-season pest of evergreen plants. This mite prefers broadleaf evergreen plants such as holly, laurel, camellia, azalea, and rhododendron. These mites are active in the spring and fall with most individuals going dormant with high summer temperatures. Feeding injury causes stippling of foliage. Foliage may take on a reddish-bronze appearance. Overwintering eggs are laid on the undersides of leaves.

Slide 41 - Two-Spotted Spider Mite: The two-spotted spider mite is a warm-season pest with a wider host range than any other mite. These mites are active from earliest spring to late fall. Feeding injury causes stippling of foliage with premature leaf drop occurring on heavily infested plants. Adult females overwinter in ground litter or under bark of shrubs and trees.

Slide 42– Internal Feeders: The next series of slides will give examples of some of the most common internal feeding pests.

Slide 43 – Leafminers: Leafminers are a diverse group of insects that includes flies, beetles, moths, and sawflies. They feed on the soft inner tissue between the upper and lower leaf surfaces creating serpentine or blotch leaf mines. Systemic insecticides will help to control leafminer problems.

Slide 44 – Boxwood Leafminer: The adult boxwood leafminer is a small, orange, gnat-like fly and is considered the most serious insect pest of boxwood. Feeding injury by the yellow larvae causes small, blistered blotches to appear on the leaves.

Slide 45 – Maple Petiole Borer: Healthy green leaves falling from maple trees during May and June, is a good indication of maple petiole borer activity. The adult female sawfly uses her ovipositor to puncture the petioles and lay a single egg near the leaf blade. Tunneling and feeding by the larvae weakens the petiole, causing the leaf to drop to the ground. The leaf drop seldom causes injury to the tree and control measures are usually not needed. Larvae continue to feed in the portion of the petiole remaining attached to the twig for seven to ten days. The larvae then drop to the ground and burrow into the soil to overwinter and pupate and emerge the following spring as mature adults.

Slide 46 – Peachtree Borer: The peachtree borer is a day-flying moth that belongs to a large group of tree and shrub pests called clearwing borers. Female moths lay eggs on the lower trunk or on weeds, grass, debris, and bare soil around the trunk. Eggs hatch in about a week and the larvae immediately burrow through the bark into the sapwood of the tree. Wounds and breaks in the bark are not need as the larvae are capable of chewing directly through the bark. Large masses of gum, particles of bark, and frass at the base of the plant are evidence of an infestation. There is usually one generation with adults emerging over an extended period that may range from late spring to early fall.

Slide 47 – Dogwood Borer: The dogwood borer is found throughout the area where flowering dogwoods are grown. Female moths lay eggs next to wounds and breaks in bark on the trunk and limbs. Newly hatched larvae enter through wounds, calloused areas, cankers or some other break in the bark. Sapstain, fine frass on the trunk and branches, and loose bark are indicators of borer activity. Badly infested trees usually appear unhealthy and may have dieback in parts of the crown. There is usually one generation with adults emerging over an extended period from late April to mid-October.

Slide 48 - Metallic Wood-boring Beetles: Metallic wood-boring beetles are probably the most damaging pests of trees in the nursery and the landscape. The adults are slightly flattened and often have a metallic sheen. Of the nearly 700 North American species, most prefer weakened, injured, dying, or recently dead trees. A few species attack healthy trees. Newly transplanted ornamental trees and shrubs are particularly susceptible to attack. Larvae usually feed and create winding tunnels just under the bark, which may girdle and kill trees.

Slide 49 – Flatheaded Borers: The larvae of metallic wood-boring beetles are called flatheaded borers because of the flattened enlargement just behind the head. Areas of bark where injury has occurred often appear darkened, somewhat sunken, and may later split above the injury. Severely injured trees may have large areas where bark has fallen off. D-shaped exit holes in the bark indicate where mature adult beetles have emerged.

Slide 50 – Longhorn Beetles: Longhorn beetles vary in size and color, but their very long antennae are characteristic of most species. There are over 900 species of longhorn beetles in North America, but only a few species seriously damage living trees. Weakened, injured, dying, or recently felled trees are usually attacked. The most harmful species bore into the heartwood and cause defects that seriously degrade lumber.

Slide 51 - Roundheaded Borers: The larvae of longhorn beetles are called roundheaded borers because of the enlarged thorax directly behind the head. All parts of the tree may be attacked including terminal shoots, branches, trunk, and roots. Some species require 2 to 3 years to complete their life cycle. Tunneling into the heartwood by the larvae may structurally weaken trees.

Slide 52 – Bark Beetles: Bark beetles are very small beetles ranging from 1/16 to ¼ inch in length and brown to black in color. Adult beetles bore through the outer bark to the phloem layer, where they channel out galleries in which to lay eggs. Larvae hatch in these galleries and may excavate additional channels as they feed. As a general rule, bark beetles attack trees that are weakened or dying due to various stress factors, including drought, disease, and mechanical injury.

Slide 53 – Asian Ambrosia Beetle: Unlike other bark beetles which feed directly on the host tree, Asian ambrosia beetles feed only on fungi they introduce to the host tree. The ambrosia fungi growing in the tunnels may disrupt the xylem tissue causing additional stress to the tree and possible death. Infestations normally can be identified by toothpick-like spines of boring dust protruding from holes made in the host plant by females excavating their galleries. Ambrosia beetles attack both healthy and unhealthy trees.  

Slide 54 – Galls: Galls are unusual plant growths caused by feeding or egg-laying activity of certain insects or mites. The gall's form depends on what organism is attacking the plant and where it is attacking. Most galls do not damage plants except for disfiguring the plant parts. Bladder galls and spindle galls are caused by mites. Eyespot galls are caused by small flies called midges.

Slide 55– Galls: Leaf galls are of little consequence to a healthy tree. Stem and twig galls are more serious and may disrupt plant functions by girdling the small branch.

Slide 56 – In Conclusion: It would be difficult to identify all of the insect and mite pests that attack ornamental plants in Tennessee landscapes, but it would not be difficult to recognize the various types of damage caused by different types of insects and mites. Knowing the host plant and the type of damage is the first step in determining the pest. Your Master Gardener handbook provides additional information about plant pests and should be used as a valuable reference. University of Tennessee Extension fact sheets and publications can be found on the web at: utextension.utk.edu

Slide 57 – The End

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