Researchers from the University of Maryland and the U.S. Department of Agriculture recently completed the first comprehensive, multi-year study of honey bee parasites and disease as part of the National Honey Bee Disease Survey. The findings reveal some alarming patterns, but clearly indicate that the frequency of varroa mite infestation is far higher than previous estimates and that it is closely linked to several damaging viruses. The results, published online in the journal Apidologie on April 20, 2016, provide an important five-year baseline against which to track future trends.
The research consisted of a survey of beekeepers and samples from bee colonies in 41 states and two territories (Puerto Rico and Guam), over a span of five seasons from 2009 through 2014. The study looked at two major parasites that affect honey bees: the varroa mite and nosema, a fungal parasite that disrupts a bee’s digestive system. The study found clear annual trends in the prevalence of both parasites, with varroa infestations peaking in late summer or early fall and nosema peaking in late winter.
The study also found notable differences in the prevalence of varroa and nosema between migratory and stationary beehives. Migratory beekeepers–those who truck their hives across the country every summer to pollinate a variety of crops–reported lower levels of varroa compared with stationary beekeepers, whose hives stay put year-round. However, the reverse was true for nosema, with a lower relative incidence of nosema infection reported by stationary beekeepers.
Additionally, more than 50 percent of all beekeeping operations sampled had high levels of varroa infestation at the beginning of winter–a crucial time when colonies are producing long-lived winter bees that must survive on stored pollen and honey.
The researchers next plan to provide a similar baseline assessment for the effects of pesticides. The multi-year survey allowed for the capture of pesticides present in hives as well and so as soon as that data is analyzed the results will be published, adding another piece to the puzzle of identifying the primary causes of declines in honey bee health. The University of Maryland work was supported by the United States Department of Agriculture’s Animal and Plant Health Inspection Service.
With increasing frequency, activists point to neonicotinoids as the primary reason that pollinator populations are on decline. However, this study and many similar research efforts call into question the efficacy of that claim. More and more scientific inquiry is emerging that underlines the fact that colony collapse disorder and dwindling honey bee populations are the result of a multitude of contributing factors. NALP and our members understand the importance of pollinators and strongly support research efforts that objectively examine the true causes of honey bee and other pollinator population and health declines.