Pest description and damage One of the blister beetles, the black oil beetle is a predator of all larval stages of the alkali bee, destroys eggs and feeds on host resources. Black oil beetles (8-18 mm) are wingless with large abdomens. Adults emerge from alkali beds late February to early April and feed on various neighboring plants. The mated female lays about 3,000 eggs in the ground. The first larval instar of the black oil beetle, an active triungulin, climbs onto a plant and attaches onto visiting alkali bees, hitching a ride back to the bee nest. The beetle larvae consumes the cell provisions in the bee nest and during its last larval stage it digs through the soil to find and eat at least one bee larva. Then the beetle larvae burrows deeper into the ground and roughly 17% remains inactive for up to 2 years while the other 83% continue to pupate and emerge as adults.
Control primary weeds in and around alfalfa fields to reduce the likelihood of blister beetles establishing themselves along field margins and migrating into alfalfa fields.
A ditch 4-6 inches wide and 6-10 inches deep can be dug around the bee bed and lined with plastic as a pitfall trap for emerging adult beetles. Insecticide can be sprayed into the ditch and the beetles will be trapped in the insecticide and die.
For more information:
C. Johansen, D. Mayer, A. Stanford, and C. Kious. 1982. Alkali Bees: Their Biology and Management for Alfalfa Seed Production in the Pacific Northwest. Washington State University. Pacific Northwest Extension Publication 0155.