Effects of chronic dietary thiamethoxam and prothioconazole exposure on Apis mellifera worker adults and brood.

Background: Chronic exposure of honey bees (Apis mellifera Linnaeus) to the neonicotinoid thiamethoxam and the fungicide prothioconazole is common during foraging in agricultural landscapes. We evaluated the survival and hypopharyngeal gland development of adult worker honey bees, and the survival of the worker brood when chronically exposed to thiamethoxam or thiamethoxam and prothioconazole in combination.

Results: We found that 30 days of exposure to 40 μg kg of thiamethoxam significantly (P < 0.001) increased the frequency of death in worker adults by four times relative to solvent control. The worker brood required 23 times higher doses of thiamethoxam (1 mg L or 909 μg kg ) before a significant (P = 0.04), 3.9 times increase in frequency of death was observed relative to solvent control. No additive effects of simultaneous exposure of worker adults or brood to thiamethoxam and prothioconazole were observed. At day 8 and day 12, the hypopharyngeal gland acinar diameter was not significantly different (P > 0.05) between controls and adult workers exposed to thiamethoxam and/or prothioconazole.

Conclusion: These results indicate that chronic exposure to field-realistic doses of thiamethoxam and/or prothioconazole are unlikely to affect the survival of adult workers and brood. © 2019 Society of Chemical Industry.