Blister Beetles

There are three types of blister beetles that may cause damage to trees and shrubs on the prairies. Larvae overwinter in the soil while adult beetles are present from May to July. The adults are long, slender, beetles measuring 12 to 28 mm in length. They may be grey, shiny black or a metallic purple with a green tinge. In the fall, eggs are deposited in the soil where the larvae develop by feeding on grasshopper and other insect eggs.

Damage

Blister beetles can be both destructive and beneficial insects. The insect is destructive during the adult stage when it causes defoliation, and beneficial during the larval stage when it feeds on grasshopper eggs. The adult beetles seem to invade in swarms and devour the foliage of host plants. Infestations are often localized and the beetles can disappear as quickly as they appear. The beetles can cause complete defoliation of young ash and caragana shelterbelts, which results in a reduction of annual growth but no permanent damage. Blister beetles can also cause extensive damage to garden plants.

Control

If an infestation occurs in a garden or on a few trees, control can be achieved by picking the beetles off the plants. Products are available to control the insect, but before spraying, consider the potential loss of pollinating bees during spraying and the beneficial aspects of the beetle during the larval stage. If chemical control is used, spray foliage and insects with: carbaryl; deltamethrin or methoxychlor.