Lethal and sub-lethal effects of colony-relevant doses of pesticides on in vitro-reared honey bees (Apis mellifera L.)

Honey bees are crucial to the proper pollination of many agricultural crops globally. The decline of managed honey bee populations in many areas worldwide has threatened global food security and has been said to result from a combination of causes. Of these possible causes, pesticides are of particular concern due to the frequency and abundance of residues identified in managed honey bee hives. Over 120 different pesticides have been identified in nectar, pollen, and wax. Using an in vitro rearing technique, we examined the effects of colony-relevant doses of pesticides, i.e. pesticides and doses documented in pollen and wax collected from colonies, on immature honey bee worker survival, development and physiology. Our target pesticides included three acaricides (amitraz, coumaphos, fluvalinate), two insecticides (chlorpyrifos, imidacloprid), one fungicide (chlorothalonil) and one herbicide (glyphosate). Each pesticide was integrated into the larval diet and fed throughout each larvae’s development. We found a significant reduction in honey bee survival (proportion of treated larvae reaching adulthood) in bees fed pesticide concentrations found in wax for all seven pesticides and concentrations found in pollen for coumaphos, fluvalinate, amitraz, chlorothalonil, and chlorpyrifos. Immature bees fed pesticides also were impacted sub-lethally. For treated bees reaching adulthood, we observed delayed pupation and adult emergence when fed amitraz (pollen concentration), chlorothalonil (wax/pollen), chlorpyrifos (wax/pollen), coumaphos (pollen), and fluvalinate (pollen). The weight of adults at the time of emergence was significantly reduced when the larvae were fed amitraz (wax/pollen), chlorothalonil (wax/pollen), and chlorpyrifos (wax/pollen). Currently, we are identifying the impact of these pesticides on developing bees by measuring detoxification and stress response genes, midgut cells damage at three developmental time points (larvae, prepupae, adult), and hypopharyngeal gland size and antennal topography in the adult workers.