Podosesia syringae

Alias: The lilac borer or ash borer is a member of the moth family that resembles a paper wasp. It is usually dark with orange, brown and yellow markings throughout its body. Adults lay eggs on the bark of trees and shrubs, and the pupa will bore into the trunk of the branch. Once inside, it is well protected and feeds until it is ready to emerge. As it emerges, it leaves small borer holes throughout the trunk that are approximately a quarter-inch wide.

Crimes: It is known for attacking lilacs, ashes and members of the olive family. They tend to prefer feeding in the lower trunk, where heavy infestations can girdle the tree. Damage can kill trees quickly in a few weeks or may take several years.

Redeeming Qualities: They do attack Russian olive trees. They are not making a dent in the population, but it makes me feel better knowing something is attacking them.

Sentence: Pheromone traps can be placed to attract males and reduce breeding. Pruning infected branches may also work if said branches are burned on site. Debris and mulch may still produce adults. If borer holes are detected with larva inside, they can be killed with a rod or wire inserted into the hole. They are susceptible to a wide range of insecticides including pyrethroids and Bt, but you must make contact with them before the larva have inserted into the tree. Insecticides must be applied in the spring before eggs hatch or in the fall after adults have emerged. Remember to always read and follow the label instructions when applying pesticides.

For more information on dangerous and beneficial bugs, call UI Extension educator Joseph Sagers at 208-745-6685 or email jsagers@uidaho.edu.