Physoconops fronto
Zodion obliquefasciatum
Pest description and damage The two species of thickheaded conopid flies are internal parasites of only adult alkali bees. Adult flies are reddish in color and about half the size of alkali bees, with a large distinct head and large eyes. Female conopids perch near nest holes waiting for returning forager bees. As the female bee approaches the nest bed, the conopid dives down and inserts an egg in the bee abdomen. Eggs hatch in one day and larvae feed internally on host tissue then overwinter and pupate inside the bee. Infested bees may continue to provision cells with pollen and lay eggs however eggs are either non-fertile or so malnourished they are unable to hatch. The presence of numerous sealed cells in bee beds that contain pollen provisions, but no larvae may be indicative of high infestation levels by parasitic conopid flies. Infested adult bees weaken as the fly larvae matures and the fly emerges from its pupal case during the same period of bee emergence the following spring. Parasitism usually occurs during the mid to late season and eventually results in reduced longevity and decreased progeny of the bee.
Management - sticky traps
The perch-and-wait behavior of conopids has been used against them, so stakes banded with Tanglefoot, or other sticky substance are set in a 10 x 20-foot grid pattern in large beds or 10 feet apart in rows placed close to the bee nest. A yellow sticky card stapled on top of the stake is a cheap and efficient solution.
For more information
Cane J.H. 2024. The Extraordinary Alkali Bee, Nomia melanderi (Halictidae), the World's Only Intensively Managed Ground-Nesting Bee. Annu. Rev. Entomol. 2024. 69:99-116
Stephen W.P. 1959. Maintaining Alkali Bees for Alfalfa Seed Production. Station Bulletin 568. http://ir.library.oregonstate.edu/concern/administrative_report_or_publi...
Walsh, D.B. and R.A. Boydston. Integrated pest management on alfalfa seed: a two-year report 2008-2009. https://ir4.cals.ncsu.edu/fooduse/PerfData/2903.pdf