Pest description and damage The bomber fly is an external parasite that feeds on mature alkali bee larvae. Bomber flies are very hairy, similar in size to the alkali bee, and usually brown to white in color with black and yellow to cream strips on the abdomen which mimic the patterning of bees (they are also known as the Bee Fly). Bomber larvae are C-shaped, brown, leathery, and about the same size as alkali pre-pupae. Female bomber flies flick eggs down or near alkali nest entrances. Newly hatched bomber flies move into the bee cells but do not feed until the alkali bee matures or is at the prepupal development stage. Each bomber fly larva will consume the bodily fluids of one alkali bee larva before moving out of the cell and overwintering near the soil surface. Pupation occurs in the late spring and adults emerge out of the soil surface.
The parasitic flies emerge in the early morning hours but cannot fly. The most effective control measure is to walk the alkali beds between 9 am and 12 noon for a two-ree three-week period beginning just before the emergence of alkali bees, killing flies with a fly swatter or by stepping on them. Shallow rototilling may reduce fly larvae numbers since fly larvae overwinter 1.25 inches shallower than bees. This may, however, pose a higher risk to bees. Alternatively, maintaining sparse weed or light grass ground cover about four inches tall can reduce the rate of parasitism. Well populated bee sites can also provide effective defense because dense bee flights will deter oviposition by flies.
For more information:
Cane, J.H. 2008. A native ground-nesting bee (Nomia melanderi) sustainably managed to pollinate alfalfa across an intensively agricultural landscape. Apidologie, 39(3), 315-323. https://doi.org/10.1051/apido:2008013