The combined effects of miticides on the mating health of honey bee (Apis mellifera L.) queens

The honey bee, Apis mellifera L., plays a pivotal role in the US economy, contributing an estimated $17 billion annually, primarily through crop pollination. Despite their importance, the number of managed honey bee colonies available for pollination services has dropped dramatically during the last decade, threatening crop yields across the country. One of the main culprits of such declines is the varroa mite, Varroa destructor, a pest of honey bees that, when present in high numbers inside a hive, causes colonies to collapse and die. For almost 20years, varroa mites have been controlled primarily with two in-hive miticides: the pyrethroid tau-fluvalinate (Apistan) and the organophosphate coumaphos (Checkmite+). Various studies have revealed that the exposure of honey bee colonies to sublethal levels of these chemicals can lead to colony-wide health problems. In this study, we looked at the combined effects of fluvalinate and coumaphos on the reproductive health of honey bee queens. We did so by raising queens in either miticide-free beeswax or beeswax containing known concentrations of both coumaphos and fluvalinate. Upon their emergence and successful mating, we took several standard measures of queen's reproductive health. We found that queens reared in miticide-laden beeswax were not significantly smaller in size, but the spermatheca analysis showed significantly lower sperm counts and viability, and higher mating frequency, compared to queens reared in miticide-free beeswax. Our results indicate that exposure to miticides during development severely compromises queen's reproductive health. Our findings also demonstrate the importance of the potentially detrimental combined effects of common in-hive miticides on colony health.