Effects of the insecticide acetamiprid and the fungicide azoxystrobin on locomotion activity and mushroom bodies of solitary bee Centris analis.

Pesticide use is a major factor contributing to the global decline in bee populations. Sublethal effects, such as behavior alterations, are neglected in pesticide regulation for pollinators. However, these effects can bring important information to understanding the impacts of pesticides on bees' daily activities. In this study, we aimed to investigate the effects of the insecticide acetamiprid (7 ng/μL) and the fungicide azoxystrobin (10 ng/μL) on the behavior of the Neotropical solitary bee Centris analis. Female and male bees were exposed to these chemicals continuously for 48 hours, followed by an additional 48 hours without contaminated food, totaling 96 hours of observation. We used five experimental groups: control, solvent control, insecticide, fungicide, and pesticide mixture (insecticide+fungicide). Behavioral alterations based on locomotion and light response were assessed by video tracking at 48 (end of pesticide exposure) and 96 hours (end of bioassay). In addition, after recording bees at 96 hours, the individuals were anesthetized for brain collection and histological evaluation of mushroom bodies to evaluate if pesticides can damage their neurons and impair the cognitive processes and responses of bees to sensory stimuli. Bees exposed to acetamiprid and pesticide mixture showed lethargic movements and impaired locomotion at 48 hours. Notably, these behavioral effects were no longer evident after the bees consumed uncontaminated food for an additional 48 hours, totaling 96 hours from the start of pesticide exposure. Only fungicide exposure did not result in any behavioral or brain histological changes. Therefore, our study showed that acetamiprid at an estimated residual concentration, despite being classified as having low toxicity for bees, can cause significant initial locomotion disruption in solitary bees. These findings highlight the importance of considering sublethal effects in environmental risk assessment.

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Declaration of Competing Interest ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: