Alkali bee-Thickheaded conopid fly

Physoconops fronto

Zodion obliquefasciatum

Pest description and damage The two species of thickheaded conopid flies are internal parasites of only adult alkali bees. The conopid adult are reddish in color and are about half the size of alkali bees, with a large distinct head and large eyes. Mated female conopids perch near nest holes and wait for returning female alkali bees. As the female bee approaches the nest bed, the conopid dives down, penetrates the bee with its ovipositor and deposits an egg into 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

Yellow and white stakes banded with Tanglefoot or other sticky substance set in a 10 x 20 foot grid pattern in large beds or 10 feet apart in rows placed on edges of beds. To minimize possibility of trapping bees apply sticky band at least two inches below the top of each stake. Stakes should be put out before alkali bees emerge so bees can establish a flight pattern to avoid traps. Stakes should also be cleaned and sticky coating reapplied weekly.

For more information:

Stephen W.P. 1959. Maintaining Alkali Bees for Alfalfa Seed Production. Station Bulletin 568.

Walsh, D.B. and R.A. Boydston. Integrated pest management on alfalfa seed: a two-year report 2008-2009.