Different concentrations of the insecticide thiamethoxam affects the midgut, behavior, and causes oxidative stress in the stingless bee <i>Partamona helleri</i> Friese, 1900 (Hymenoptera: Meliponini)

Approximately 30% of global food production relies on crops that depend on pollinators. In the Neotropics, Meliponini bees are generalist pollinators, contributing to the pollination of up to 90% of the native flora. Partamona helleri is a eusocial stingless bee that plays a crucial role in pollinating several economically significant plants. However, various factors, particularly exposure to insecticides, are driving the population decline of these insects. Thiamethoxam is a neurotoxic neonicotinoid that acts on nicotinic acetylcholine receptors but can also affect other organs, such as the midgut, through ingestion. This study assessed the effects of acute oral exposure to thiamethoxam on the behavior, midgut, and oxidative stress of P. helleri workers. The bees were orally exposed for 72 hr to sublethal concentrations (LC) of thiamethoxam corresponding to LC5 and LC50. The results revealed that thiamethoxam exposure altered the bees' behavior, affecting their traveled distance and meandering activity. Additionally, the insecticide caused histopathological alterations in the midgut epithelium of workers, including cytoplasmic vacuolization, nuclear pyknosis, and release of cell fragments to the gut lumen secretion. Both LC5 and LC50 concentrations induced oxidative stress, as evidenced by changes in detoxification enzyme activity and antioxidant markers. These findings indicate that sublethal concentrations of thiamethoxam negatively impact P. helleri workers, potentially compromising individual survival and colony health.