Clearwing moth larval feeding can cause tree bark to become gnarled or rough. Borer feeding can damage the plants food- and water-conducting tissues. With some clearwing species such as those that attack sycamore and pine, feeding is tolerated by trees and apparently causes no serious harm. Feeding by other species can weaken or kill branches. Branches weakened by larval tunneling may break and fall, especially during windy weather. Sometimes entire trees may die. Other types of wood-boring insects produce similar damage.
Mature woody plants usually tolerate and can recover from the attack of a few clearwing moth larvae. However, the presence of this pest often indicates that plants have been injured, stressed, or neglected. Providing trees with appropriate cultural care is the primary damage prevention strategy. Sometimes larvae can be killed by puncturing or crushing them. Heavy infestations of clearwing moths may warrant treatment with beneficial nematodes to kill larvae, broad-spectrum insecticides to kill adults, or both.
Traps containing clearwing moth sex attractant (pheromone) are used primarily for monitoring. However, continual dispersion of clearwing moth pheromone throughout the mating season to reduce the ability of the adult moth to mate (a process called “mating disruption”) has been found effective in reducing peachtree borer populations and injury in orchards in the eastern United States. Mating disruption is relatively expensive and labor intensive, and apparently has not been investigated in landscapes.
Because other wood-boring insects produce damage resembling that of clearwing moths, correctly identify the cause before taking control action. If insecticide applications are planned, use traps to monitor moth emergence, inspect bark for fresh pupal cases, or both.
Immediately before adult moths emerge, clearwing pupae often force about half of their length out of a tunnel and through the surface of damaged bark. Carefully inspect around damaged bark at least once each week, starting before adult emergence is expected. Look for fresh clearwing moth pupal cases protruding from bark, in tree crotches, and around the base of trees. Because old pupal cases can persist for months, remove these when found and monitor frequently with care to ensure that any pupal cases observed are new. This trunk inspection method does not work with peachtree borer because larvae drop from tunnels and pupate in soil around tree bases.
Traps baited with a pheromone (insect sex attractant) are available for certain clearwing moth species, including ash and peachtree borers. Male clearwing moths drawn to the pheromone dispenser become caught on the traps sticky coating. If a pheromone is available for the clearwing borer species of concern (see Pheromone Trap Suppliers at the end of this publication), hang a trap containing the pheromone about shoulder high on each of two or more trees spaced at least several hundred feet apart. Follow the manufacturers recommendations for maintaining the trap, such as the frequency with which pheromones should be replaced. Commercial traps typically attract more than one species of clearwing. Identify trapped moths and be certain they are species that attack your trees before you decide to take control action.
Because moths can be attracted from great distances, traps need not be located in infested trees, but may be placed where they are more convenient to monitor. Check the traps once a week for moths. To help you identify whether the moths are a species that attacks your plants, use the photos here and in Pests of Landscape Trees and Shrubs. You may also take the trap containing your moths to your county Cooperative Extension office for identification. Save the identified moths for comparison when additional moths are captured.
Clearwing moths may be captured in traps almost any time during the growing season. However, each species typically flies in numbers during only a few weeks or months each year. Ash borer and redbelted clearwing adults in California fly from April through July. Peachtree borer, sycamore borer, and western poplar clearwing adults are active primarily from May through July. In southern California western poplar clearwing adults have been found in November and February through May. Male moths emerge first and fly primarily around dusk. Females are ready to mate and lay eggs almost immediately after they emerge.
Make sure trees receive appropriate irrigation. Provide good soil conditions. Protect roots, trunks, and limbs from injury. Keep weed trimmers and lawn mowers away from trunks; using a mulch or a ground cover in a several-foot-wide area around the trunk will keep the area free of turf and other vegetation and eliminate the need for mowing. Stake young trees only if needed to protect or support the trunk or anchor the root ball during the first year or so after planting.
Clearwing moths are attracted to tree wounds. Avoid pruning live branches unless necessary to develop tree structure or remove severely infested, dying, or hazardous limbs. Except for hazardous limbs that should be removed whenever they appear, prune only during fall through early winter to minimize the chance of attracting egg-laying moths.
Kill peachtree borers and possibly larvae of other clearwing species by carefully using a knife or stiff wire to probe the trunk during spring or fall where gummy frass exudes from bark. It is difficult to know whether the larva has actually been killed by being punctured or crushed. Reinspect trunks in a week and again probe tunnels if fresh gum exudate is observed, indicating a live larva is present. Minimize injuries to bark when probing tunnels. Do not create large wounds in cambial tissue.
Where peachtree borer is a problem, remove suckers and keep vegetation and mulch away from the base of the tree. Bare soil around trunks increases the likelihood that any tunneling will be observed. In the Central Valley, bare soil around trunks increases heat and dryness. This reduces survival of borer eggs and larvae and can prevent peachtree borer from becoming a pest.
If high-value trees are infested, insecticide can be applied to bark when egg-laying moths are active to reduce future infestations by some clearwing species, including the ash borer, peachtree borer, and western poplar clearwing. If extensive portions of the tree are already dead or trees are heavily infested with borers, spraying may provide little or no benefit and the tree may need to be removed.
Only certain broad-spectrum, long-lasting insecticides are effective in preventing borer attacks. Effective products may not be currently available for home users, although they are available to licensed pest control applicators. The pyrethroid permethrin is the best choice for preventing clearwing moth attack. Spray residue must persist for weeks to several months in order to kill adults before they lay eggs or kill hatching larvae before they bore into wood. Insecticide sprays have not been found to be effective against borer larvae beneath bark. Soil or trunk injections of systemic insecticides are not effective either. Trees may continue to decline unless insecticides are used in combination with improved tree care practices.
To be effective, a bark spray must be carefully timed. Determine when moths are emerging by frequently examining trunks and limbs, by inspecting pheromone-baited traps, or both, as discussed in the section on Monitoring, above. About 10 to 14 days after you first detect adults (catch pest moths in traps or observe fresh pupal cases), apply an insecticide to the main trunk, on top and underneath limbs where they join the main trunk, and on wounded bark of susceptible trees. There is no need to treat foliage, especially in the upper canopy. Apply sufficient spray to thoroughly wet the bark. For peachtree borer, allow spray to run down the lower trunk and thoroughly wet the soil within several inches of the tree base. (Do not allow pesticide to drip down on to hard surfaces beneath or adjacent to trees since this can lead to runoff and water contamination.) If moths continue to emerge or to be found in traps for longer than about 1 month after the application, spray again. The following year treat once or twice to further reduce the infestation.