Effects of commonly used agrochemicals and their interactions on honey bee (Apis mellifera) colony health

Recent annual honey bee colony losses (averaging 30%) are alarming to both beekeepers and growers, who are interdependent for their economic viability. Pesticides are presumed to play a significant role in the colony declines, but impacts of pesticides on honey bee health are not well understood, with insufficient literature on this topic to make conclusive interpretations. There is a high demand for data on the colony-level impacts of pesticides in field-realistic doses, which are crucial in order to make proper inferences. This experiment will provide a comprehensive understanding of how two widely used agrochemicals (imidacloprid and chlorothalonil) may impact colony health and immune capabilities, both separately and in conjunction with each other.

Experimental colonies were provided pollen patties containing these chemicals, at concentrations previously found in stored pollen, for four weeks. Multiple colony-level parameters were measured before and after feeding at regular intervals. Mean parasite loads and mean changes in colony size (adult bees), brood area, pollen stores, and honey stores, were not significantly different between the treatments during the ten-week period since initiation of the experiment. The number of foragers (pollen and non-pollen) were also not significantly different between treatments. The preliminary results show no significant colony-level effects of these pesticides when consumed in pollen; however, data pertaining to physiological parameters and immunity assays (phenoloxidase activity, prophenoloxidase activity, glucose oxidase activity, midgut enzyme activity, and hypopharyngeal gland protein) are still being analyzed and quantified. Overwintering success of these experimental colonies will also be recorded in the following spring.