Heterostylum robustum
Pest description and damage The bomber fly (family Bombyliidae) is an external parasite that feeds on wild and managed alkali bees. Bomber flies are very hairy, similar in size to the alkali bee, and display pattern colors that mimic bees. Female bomber flies loudly hover over nest aggregations and flick eggs down or near alkali tunnel entrances and soil cracks. Newly hatched flies move down 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. Bomber flies typically consume 20-40% of alkali bee larvae. Pupation occurs in the late spring and adults emerge out of the soil surface.
Management-cultural control
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 to three-week period beginning just before the emergence of alkali bees, and growers traditionally paid children to do so. It is not uncommon to see birds have a feast on recently hatched flies. 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