Pest Identification & Damage
Common Name(s): Clearwinged Moths, Sessiids
Scientific Name:
Family Sessiidae.
Identifying Characteristics for Damaging Stage(s):
Clearwinged borers belong to the order Lepidoptera, and the larval stages are typical caterpillars, whose eggs are laid by adult moths. Clear-winged moths are daytime fliers and otherwise appear very similar to wasps in coloration, having four somewhat tapered wings held wasp-like over the body when at rest. Their bodies may be drab or brightly marked, either with yellow and black or black and red, or purple and white. And their flight behavior is very wasp-like. However, their forewings are covered with overlapping scales, while the hind-wings are clear and transparent.
The larvae of clear-winged moths are typical caterpillars - white, with 6 short, segmented legs just behind the head, with 4 pairs of fleshy prolegs on the abdomen. Size may range from one eighth to about 1 inch, depending on degree of maturity. Once larvae penetrate beneath bark and enter the wood, they begin to expand galleries, pushing coarse wood fragments and frass to the outside. The pupa of several species may push itself through, and be partially exposed in the exit hole just prior to emergence.
Damage/Nature and Symptoms:
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| Damage to Crown of Lilac |
Clearwinged borer caterpillars mine throughout stems, branches or trunks. Mines are dirty in appearance and packed with frass mainly consisting of fecal pellets. Old exit holes may be evident, and new tunnels that open to the surface may discharge sawdust, feces and sap. Infested branches, crowns or canes may be swollen or cracked, with an irregular bark texture.
Borers attack nearly all trees and shrubs to some degree, but certain species are more susceptible to infestation. Newly set tree plantings, including fruit orchard species are highly susceptible during the first years when they are under stress. Establishment and root system development is a critical time for new trees and they must be carefully tended, well-watered, fertilized and protected from borers during this period.
To understand how boring insect damage trees and shrubs, it is essential to know the basic fundamentals of tree growth. Trees grow in height because of apical buds, or meristems at the tips of twigs, which results in extending these stem tips. Trees grow in width, or girth because of a special ring-like meristem, consisting of several tiers of cells, perhaps just 8 - 10 cells in thickness, the cambium layer, which surrounds each stem, including the main trunk itself. If these cells are killed, for example by cutting around the girth of a tree with a chainsaw, or by the feeding of insects beneath the bark we know that the tree is "girdled" and will die. These meristems are the living parts of the tree both wood and bark cells are technically dead, although they may continue to function by conducting water and nutrients. The cambium produces wood (or xylem) cells to the inside and bark (phloem) cells to the outside. The cambium grows rapidly each spring, when day length is increasing and water is more plentiful, producing large wood cells to the inside. Later in summer, when day length is beginning to
shorten and moisture is in shorter supply, growth rate slows and the cells produced are smaller. As winter approaches, growth stops altogether, to be resumed in the spring. These differential
growth rates in spring, summer and fall, producing differently sized cells, accounts for the annual growth rings. The outermost (most recent) growth rings constitute the sapwood, whose cells are
usually higher in starch or sugar content and are therefore often more attractive to certain types of insect larvae. In the middle of a mature tree, the oldest growth rings appear darker and the cells
may be more thickened or lignified and less attractive for insect feeding. This heartwood is sometimes chosen for use as posts and other wood that may have soil contact because it is somewhat more resistant to the feeding of certain insects.
Distribution and Life Cycle
Distribution:
Clearwinged borers have varying ranges across the United State, depending upon the species. Many are host-specific and occur only where their host plants are distributed. Examples of more common clearwinged borers are, ash borer, banded ash clearwing, red oak clearwing, cottonwood clearwing, American hornet moth, hornet moth, peachtree borer, dogwood borer, willow clearwing and viburnum borer.
Representative Species:
Lilac and Ash (Privet) Borers:
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| Lilac Borer Moth and Pupal Skin |
Adults of lilac and ash (privet) borers, Podosesia syringae syringae (Harris) and P. syringae fraxini (Lugger), are day-flying, clear-winged moths that resemble wasps, emerging
from infested hosts in May and June. After mating, the adult females deposit eggs on the lower portions of the trunks or branches of ash, lilac or privet. The caterpillars bore into and feed within
the stems and winter as partly grown larvae. If larvae are abundant or canes are small, feeding may cause leaves to yellow and wilt in late summer. Coarse chewings, often referred to as "frass" or excrement, are produced by boring caterpillars, and this material is pushed out from the burrows. Infested canes of lilac or privet may be heavily scarred and swollen near their bases, and may eventually die. Severely infested stems should be cut at ground level and destroyed each spring. The borer spends the winter in the pupa stage and there is only one generation each year.
The ash borer adult is essentially identical in appearance to the lilac borer, with brown forewings and transparent hindwings. The adult is also a day-flying, clear-winged moth that resembles a
wasp. Adults emerge in June or July and deposit eggs on the bark of both ash and privet. There is just one generation each year.
Management Methods:
Inspection/Survey Methods:
It is important to regularly check young trees and shrubs that are becoming established in the landscape. Also, inspect the bases of trees for signs of oviposition (egg clusters in bark crevices or wounds), or for emergence holes from which adults recently emerged.
For detection of adult moths, particularly in areas where infestations have been troublesome, set out a few pheromone traps (wing-style sticky traps) sometime prior to expected emergence. Lures for attracting clearwing moths in general, or those for specific pests are available through companies that specialize in supplies for Integrated Pest Management practices. In addition to detection, pheromone traps are extremely valuable in determining more precisely the timing of insecticides for control of clearwinged borer infestations.
Non-Chemical Management Strategies:
Plant trees and varieties that are less prone to borer attack, such as oaks, lindens, crab apples, and conifers. Choose trees and shrubs that are suitable for the climatic zone in which they are planted. Those more vulnerable to the extremes of winter and summer in the Great Plains will ultimately suffer damage and be attractive to borers.
Several cultural practices can reduce borer infestations. Trees that are strong and maintained in vigorous growing condition are not as attractive to borers. Trees should be properly watered,
fertilized, and protected from pests, particularly during the first two or three years of growth and during drought periods that cause extreme stress.
Trimming damaged trees and eliminating weak ones is are very important management tools. Infested limbs, branches and trunks should be trimmed in the fall, burned or chipped and composted during the winter to reduce emerging borer populations.
Borer damage must be prevented because once borers gain access to cambium, sapwood, and heartwood, little can be done to control them. A few worms may be destroyed by probing active tunnels (with emerging sawdust) with a stiff wire or by injecting some fast-penetrating petroleum material (kerosene, penetrating oil, diesel fuel) into the sawdust.
Chemical Management Strategies:
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| Spray Application of Insecticide |
Chemical treatments are effective only if applied as residual sprays prior to egg-laying activity by beetles or moths. If residuals are in place, young larvae are killed while attempting to invade the wood. While proper timing is critical, it is extremely difficult to achieve. The difficulty is in determining which trees may be infested. Normally the infested tree population is quite low, therefore routine preventive treatments are not feasible. Recently the cancellation or banning of effective residual treatments has further made the issue of timing even more difficult, since long residual products are no longer legal to use.
Follow label instructions carefully so that good control is achieved, and that humans, animals and the environment are protected.
For the latest information on available chemical controls, consult the
Pesticide Selection Guide.
References:
Baker, W. L., 1972. Eastern Forest Insects. USDA Forest Service Misc. Pub. No. 1175, US Forest Service, 642 pp.
Solomon, J. D., 1995. Guide to Insect Borers in North American Broadleaf Trees and Shrubs. USDA Forest Service Handbook #706, 735 pp.
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