Peachtree Borer, Synanthedon exitiosa
Order: Lepidoptera
Family: Sesiidae
Description
The peachtree borer is a clearwing moth that visually mimics the pepsid wasp to ward off predators.
There is strong sexual dimorphism among adult peachtree borers. Female moths have dark bodies with clear hind wings and opaque fore wings, with a wingspan around 3.5 cm (1.4 inches). Females also have one or two yellow bands on abdominal segments four and five, or just on the fourth segment if only one yellow band is present. Male moths are smaller and more slender with a wingspan of about 2.25 cm (0.9 inches); both the forewing and hindwings of males are transparent, and the abdomen has several narrow yellow bands.
Male moths typically emerge in mid-June and females emerge a couple of weeks later. Peak mating and egg laying occur in July and August. Female moths lay eggs near the base of the tree in soil cracks and on bark of the lower trunk. The eggs hatch about ten days later.
Quick Facts
- The peachtree borer (Synanthedon exitiosa) is a clearwing moth. The family Sesiidae includes around 1000 species worldwide. Unlike most moth species, clearwing moths are highly active during the day.
- Male and female peachtree borer moths are different in size and coloration.
- This species is a major pest of peaches in much of the United States and certain parts of Canada.
- The presence of wood fragments and frass in oozing sap, as well as pupal skins near the base of the trunk, are indicators of a peachtree borer infestation.
- Pheromone traps should be used to inform decisions related to chemical treatments.
Peachtree borer (Synanthedon exitiosa) larva. The peachtree borer is the most destructive pest of stone fruits (Prunus spp.) grown in Colorado. Some examples of stone fruits include plums, cherries, and peaches. Unlike many insect pests that attack the fruit directly, peachtree borer larvae feed on wood underneath the bark and produce extensive wounds that can kill the tree if left untreated. Image credit: Eugene E. Nelson, Bugwood.org
Mating pair of peachtree borers. Note the sexual dimorphism – males (left) are smaller, black with yellow stripes, and clear wings. Females (right) are larger, black with one or two wide orange bands, and black wings. Image credit: Joseph Berger, Bugwood.org
Larvae of peachtree borer on a peach tree branch. Image credit: Eugene E. Nelson, Bugwood.org
Peachtree borer pupa (top) and pupal case (bottom). Image credit: John .A. Davidson, Univ. Md, College Pk, Bugwood.org
Damage at the base of a young peach tree caused by feeding of peachtree borer larvae. Image credit: James Solomon, USDA Forest Service, Bugwood.org
Peachtree borer adults being lured to a pheromone trap. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
This species overwinters as larvae in parts of the tree below the ground and resume feeding when soil temperatures reach 10°C (50°F) the following spring. The most significant injury occurs in mid-to-late spring as the larvae feed until reaching maturity. By early June, larvae are fully grown and begin to pupate in parts of the host tree below the soil surface. Pupation occurs in cells containing silk, gum, and chewed wood. Adults emerge within a month and often pull pupal skins out when they exit the tree. These skins can sometimes be seen near the base of the trunk.
Male moths typically emerge in mid-June and females emerge a couple of weeks later. Egg laying occurs within hours of female emergence from the host tree, and adults emerge continuously over several months. Peak mating and egg laying occur in July and August, and each female lays an average of 500-600 eggs throughout her life. Most eggs are laid in bark cracks and crevices on the lower trunk of host trees, although female moths will also lay eggs on branches, twigs, and leaves of host plants, as well as nearby weeds and bare soil around the trunk of the host. The eggs hatch about ten days later, and newly emerged larvae begin crawling down the trunk and bore into the tree at or below ground level where they begin feeding on the cambium layer. This typically occurs several inches below the ground on larger roots and lower parts of the trunk. The peachtree borer produces one generation each year.
Injury
Peachtree borer infestations cause copious amounts of sap to exude from entrance holes on lower branches and parts of the trunk close to the ground. Cytospora canker is a fungus that infects stone fruits and causes sap to ooze from wounds, a symptom that resembles peachtree borer feeding injury. The presence of wood fragments and frass in sap, along with the presence of pupal skins near the base of the trunk or protruding from bark, indicate peachtree borer activity.
Peachtree borer infestations generally cause a drop in yield and most trees will die if left untreated.
Monitoring
Certain traps that emit sex pheromones are attractive to male moths. These traps can help determine the timing of adult activity and egg laying. Most egg laying occurs in July and August; however, some adults can still be present in September. Each trap consists of a plastic top and bottom connected by a wire with a lure. The inner surface of the bottom portion of the trap is coated with an adhesive to capture insects as they enter and land inside of the trap. The traps should be hung at eye level, with one trap deployed in every ten acres of trees in commercial orchards. A minimum of two traps per orchard should be used. For effective treatment, accurate identification of moths is important since other species of clearwing moth may be captured in the traps, such as the lilac/ash borer. When monitoring is not possible, preventative sprays can be applied to tree trunks.
Cultural ontrol
Healthy trees can withstand peachtree borer infestations better than stressed trees, and chemical control is ineffective once larvae become established under the bark. Therefore, trees should be planted in appropriate sites with sufficient fertilizer and irrigation. Removing vegetation from the base of trees exposes eggs and larvae to heat which reduces their survival. Destroying wild stone fruits is not recommended because adults can fly long distances in search of suitable host trees.
Larvae can be physically removed from trees with a knife or wire in late summer and fall before they cause significant injury the following spring. To do this, the top 10-12.7 cm (4-5 inches) of dirt should be removed from the base of the tree. Care should be taken to make vertical cuts and avoid cutting undisturbed bark which can further injure the tree. When finished, dirt should be replaced around the tree base to its original level.
In orchards that are relatively isolated from nearby sources of reproducing females, the use of pheromones can disrupt mating behaviors and suppress the pest population growth. Commercial dispensers of synthetic sex attractant can prevent male moths from locating and mating with females. This mechanism works by overwhelming the sensory system of the male moths and desensitizing them to the sex pheromone. The female moths remain unfertilized and therefore do not lay eggs. The use of pheromone traps is recommended to verify that this technique is working since male moths should not attracted to the sex pheromone emitted by traps.
Chemical control
Insecticides with residual activity are most effective because they remain active for several weeks and kill young larvae as they emerge from eggs. The use of pheromone traps will alert growers to moth activity and aid in the timing of sprays. Missed or poorly timed applications can lead to high levels of peachtree borer infestations, which become evident the following growing season. These preventative sprays should be applied during egg hatch. Insecticides should be uniformly applied to the tree base and lower trunk where egg laying occurs most frequently. After hatching, immature larvae become exposed to tree bark treated with insecticides. These insecticides are not effective after larvae burrow into the sapwood. A repeat application may be warranted in early August wherever peachtree borers remain active in late summer.
For more information on preventative insecticide treatments, consult the full factsheet here.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Bessen, R. 2019. Peachtree Borer. University of Kentucky – Department of Entomology. Available https://entomology.ca.uky.edu/ef200Encyclopedia Britannica. (n.d.). Clearwing Moth. Encyclopedia Brtannica. Available https://www.britannica.com/animal/clearwing-moth
Grasswitz, T., and S. Yao. 2016. Efficacy of pheromonal control of peachtree borer (Synanthedonexitiosa (Say)) in small-scale orchards. Journal of Applied Entomology. 140: 669-676. Available https://onlinelibrary-wiley-com.ezproxy2.library.colostate.edu/doi/epdf/10.1111/jen.12305
Shapiro-Ilan, D., T. Cottrell, R. Mizell, and D. Horton. 2016. Curative Control of the Peachtree Borer Using Entomopathogenic Nematodes. Journal of Nematology. 48(3): 170-176. Available https://intapi.sciendo.com/pdf/10.21307/jofnem-2017-024
Strickland, S. 2018. Featured Creatures. Available https://entnemdept.ufl.edu/creatures/fruit/borers/peachtree_borer.htm
Utah State University. (n.d.). Greater Peachtree Borer. Utah State University: Extension. Available https://extension.usu.edu/pests/ipm/notes_ag/fruit-gptb#:~:text=Adults%20are%20similar%20in%20appearance,white%20with%20a%20brown%20head.