We have two species of borers that attack trunks or branches of peach trees in New Hampshire. The most destructive (and larger of the two) is the peach tree borer, Synanthedon exitosa (Say). Lesser peach tree borer, Synanthedon pictipes (Grote & Robinson) is also here, but it creates less damage. Larvae of a third species, Oriental fruit moth, bore in the tips of twigs, so we will not cover them here. Rarely, we see peach bark beetle boring in peach trees. It is covered at the end.
Life Cycle and Damage
Peach tree borers overwinter as partially grown larvae, in a gallery under the bark. Usually they are close to or below ground level. Because the egg laying period is so long, overwintering larvae vary greatly in size. As temperatures warm up, they resume boring, and usually complete their feeding in May. Fully grown larvae are cream colored one inch (25mm) long caterpillars, with brown heads. They move close to the surface and spin their cocoons, which are usually hidden by droppings and/or particles of soil. They pupate inside their cocoons, and the adult moths emerge starting about June 10th. Sometimes the brown skin of the pupa is visible protruding from the exit hole, after the moth emerges. Adults are 15-17mm long (about 5/8 inch), shaped very much like wasps. They may get some protection from bird predation because of their resemblance to stinging insects. The males have transparent wings with a few black markings. Sometimes there is a hint of light brown on the wing membranes. The bodies of males are black with metallic blue highlights, and a few narrow pale stripes. Females have black forewings, and the rear wings are clear in the center, with black edges. Their bodies are black, with a wide bright orange band on the abdomen.
The adults are present from June 10th until August 30th, with peak numbers about July 10th to 15th. When newly emerged, females release a pheromone into the air that males use to find the females and mate. Soon after mating, the females start laying their eggs in cracks and crevices of bark, low on the trunk. Some are laid in soil very close to the trunk. These insects are strong fliers, and females are strongly attracted to lay eggs in trees that have borer or mechanical damage. The eggs hatch in about ten days, and the caterpillars bore into the bark.