Commercial apiarists and state bee inspectors now have a fast new way to check Varroa mites for this honeybee parasite's resistance to the pesticides coumaphos and fluvalinate.

Agricultural Research Service (ARS) entomologists in Beltsville, Md., have developed a “do-it-yourself” bioassay that determines, within six hours, whether Varroa mites are fully resistant to the pesticides, are approaching resistance, or are still vulnerable.

Varroa mites are blood-sucking parasites of honeybees that can weaken or destroy hives. Continuous use of coumaphos and fluvalinate to prevent such damage has prompted the emergence of resistance among some Varroa populations, according to Jeffery Pettis, in the ARS Bee Research Laboratory at Beltsville.

The ARS scientists' bioassay is intentionally low-tech. Its main parts include glass canning jars in which to contain honeybees, mesh lids through which mites on the bees can fall out and be counted, and index cards that hold strips of either coumaphous or fluvalinate.

A mathematical formula determines the mites' resistance levels or susceptibility to the pesticides.