The effects of crop protection pesticides and chemicals on honey bee (Apis mellifera) mortality

The honey bee (Apis mellifera) contributes approximately $17 billion annually in pollination services of several major food crops in the United States including almond, which is completely dependent on honey bee pollination. Every year, tens of thousands of honey bee colonies belonging to commercial beekeepers from around the country are contracted for pollination services from January to March during the almond bloom in California. Almond growers face challenges to crop productivity due to several pests and pathogens. For instance, fungicides are often applied in combination with other products to control fungal pathogens during almond bloom. The potential synergistic effects of fungicides on honey bee health are still unknown, however. To assess the effects of select fungicides used during almond bloom on honey bee mortality, we collected honey bee foragers from a local apiary and exposed them to the label dose or a range of dose variants (from 0.25 to 3X the label dose) of selected fungicides, alone and in combinations, including iprodione, Pristine® and Quadris^®. We utilized a wind tunnel and atomizer set up to simulate field-relevant exposure of honey bees to these chemicals during aerial application in almond fields. We then caged groups of 40-50 exposed foragers, as well as unexposed control groups, and kept them in an incubator with daily provisions of pollen carbohydrates (e.g. a 50:50 sucrose/water solution), and water. Forager mortality was monitored daily over a ten-day period. Our preliminary results indicate a significant increase in forager mortality resulting from exposure to the fungicide iprodione (22g/L H2O) and potential synergistic impact on forager mortality of iprodione in combination with the fungicides Pristine^® (21.8mL/L H2O) and Quadris^® (125mL/L H2O).