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 is a clearwing moth. The moth 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.
  • 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.
Peachtree borer larva

Peachtree borer (Synanthedon exitiosa) larva
Eugene E. Nelson, Bugwood.org

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.  

ptb mating pair

Joseph Berger, 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.

ptb larvae on peach tree

Eugene E. Nelson, Bugwood.org
Larvae of peachtree borer on a peach tree branch. 

ptb pupa
John .A. Davidson, Univ. Md, College Pk, Bugwood.org 
Peachtree borer pupa (top) and pupal case (bottom) 
ptb feeding injury at tree base

James Solomon, USDA Forest Service, Bugwood.org 
Damage at the base of a young peach tree caused by feeding of peachtree borer larvae.

ptb pheromone trap

Whitney Cranshaw, Colorado State University, Bugwood.org 
Peachtree borer adults being lured to a pheromone trap.

Life History and Habits

The peachtree borer has one generation a year, and only the larvae can injure trees. The larvae reach up to 3.5 cm (1.4 inches) in length and have white bodies with brown heads. They tunnel into the sapwood through gaps or wounds in the bark immediately upon hatching from the egg; this typically occurs several inches below the ground on larger roots and lower parts of the trunk. Larvae overwinter in these parts of the tree below ground and resume feeding when soil temperatures rise.

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 below the soil surface 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.

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.

When monitoring is not possible, preventative sprays can be applied to tree trunks. 

Cultural Control

Healthy trees can withstand peachtree borer infestations better than stressed trees. 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. Care should be taken to avoid cutting undisturbed bark which can further injure the tree. 

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. These preventative sprays should be 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. 

References

Encyclopedia Britannica. (n.d.). Clearwing Moth. Encyclopedia Brtannica. Available https://www.britannica.com/animal/clearwing-moth

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.

CSU Extension Fact Sheet

Download or view the CSU Extension’s PDF fact sheet for your reference.