4: Heterogeneous and dynamic pesticide exposure affects honey bee colony losses

The detrimental effects of pesticides on honey bees is a major concern to commercial beekeepers. The results discussed here are the preliminary findings of two separate two-year longitudinal studies investigating the impacts of in situ pesticide exposure in commercial beekeeping operations. We analyzed pesticide residues in stored pollen and related these to metrics of colony health such as adult bee population, area of sealed brood, stored nectar and pollen, honey production, Varroa infestation, and ultimately colony survival. Results from the first study of a stationary honey production operation in northern Iowa showed that extraordinarily high Varroa mite infestation was the overwhelming factor in colony losses in the first year and confounded the impact of pesticide exposure. Pesticide exposure was higher in the second year which resulted in higher colony losses in the summer and queen supersedure. The second study in a migratory honey production and almond pollination operation showed that the number and load of fungicides and herbicides, but not insecticides, affected many aspects of colony health and survival. These results demonstrate unique pesticide exposures across field studies which may create different syndromes of colony losses. Despite low acute toxicity, the impacts of fungicides and herbicides indicate future research should focus on these pesticide classes. Comprehensive data on each colony, especially Varroa infestation levels, should be collected to accurately evaluate the impacts of pesticides on individual factors on colony health.