Effect of in-hive miticides on drone honey bee survival and sperm viability

The survival of a honey bee colony depends, in part, on the reproductive success of the queen, which in turn depends on the viability of sperm produced by drones with which the queen mates. Colony success also depends on management of the ectoparasitic bee mite, Varroa destructor, which has historically been achieved using miticides that may also impact honey bee health. Previous work has demonstrated that the exposure of drone honey bees to miticidal Checkmite+™ strips (coumaphos) can result in decreased sperm viability. In this study we applied a range of sublethal doses of six miticides (tau-fluvalinate, coumaphos, fenpyroximate, amitraz, thymol and oxalic acid) to 1-4 day old adult drones. We returned drones to their home colony and re-collected them two to three weeks later to assess sperm viability using SYBR14 and propidium iodide stains. Counts of live and dead sperm were automated using the EBImage library in the R statistical environment. Sperm viability was not affected by any of the six miticide treatments, which suggests that acute miticide exposure in adult drones has little effect on drones' reproductive potential. However, two of the six miticides tested had an effect on drone recapture rate: fenpyroximate reduced and thymol increased the likelihood of drone recapture. These results suggest that future research on the effect of pesticides to drone sperm viability should focus on exposure in the immature stages and that beekeepers concerned with drone reproductive health may be able to safely apply miticides when only adult drones are present.