Do beekeeper applied pesticides affect pathogen levels and immunity in honey bees?

Honey bee colony losses are a continuing issue that beekeepers face each year. No single factor has been shown to cause increased colony losses. In this project, we are investigating the effects of pesticide treatments on pathogen levels and immunity factors in honey bees. Colonies were exposed to three different pesticides: chlorothalonil, a commonly used fungicide; fumagillin, an antibiotic used for Nosema control; and tau-fluvalinate, an acaricide used for varroa mite control. We collected samples of bees pre-treatment and 2 and 4 weeks post-treatment. Analysis for the fall showed that the three treatments had no significant effect on N. ceranae levels, nor did N. ceranae levels vary over time; however, there were significantly fewer N. ceranae infections 4 weeks post-treatment compared to 2 weeks post-treatment (p < 0.01). We examined phenoloxidase (POX) and glucose oxidase (GOX) as measures of individual and social immunity, respectively. POX activity did not vary across treatments but overall POX activity was significantly higher at two weeks post-treatment compared with pre-treatment activity (p < 0.01) but was not different from levels at 4 weeks post-treatment. GOX activity was not affected by any treatment or treatment timing. Furthermore, the correlation between GOX and POX was not affected by treatment or the treatment timing. Our results suggest that exposure to chlorothalonil, tau-fluvalinate, and fumagillin in the fall do not negatively affect colonies. Our study is continuing with treatments in spring and summer of 2013 to monitor possible changes over the season when honey bees face different stresses.