Chronic laboratory exposure to environmentally relevant concentrations of Mospilan 20 SP (acetamiprid): effects and molecular responses in honeybees (Apis mellifera L.)

Bees were exposed for 10 days to a sucrose solution containing acetamiprid at concentrations of 48, 4.8, and 0.48 mg a.i./kg of solution, corresponding to the maximum recommended field application rate and its 1/10 and 1/100 dilutions. An increase in mortality was observed at the highest tested concentration, with a cumulative mortality of 30.4% by day 10, whereas lower concentrations showed effects comparable to the control. In addition, the expression of selected genes related to detoxification (glutathione S-transferase, thioredoxin reductase), oxidative stress (superoxide dismutase 1, superoxide dismutase 2), immunity (abaecin, hymenoptaecin, apidaecin), and neural regulation (acetylcholinesterase 1) was analysed. No significant changes were detected in most genes, except for sod2, which showed increased expression at the lowest concentration. Overall, the results suggest that acetamiprid exhibits relatively low chronic toxicity at environmentally relevant concentrations but may induce significant effects at higher or continuous exposure levels. These findings highlight the importance of considering both lethal and sublethal endpoints, including molecular responses, in assessing pesticide risks to honeybees.