Effects of the insecticide thiodicarb on non-target organs and behavior of the stingless bee Partamona helleri (Hymenoptera: Meliponini)

Abstract

Stingless bees are vital pollinators in the Neotropics and can be exposed to pesticides used in agriculture during their foraging activities. Among these pesticides, the insecticide thiodicarb is commonly applied to bean and sunflower crops, posing a potential risk to the stingless bee Partamona helleri, which pollinates these plants. This study aimed to investigate the effects of thiodicarb on mortality, morphology, programmed cell death signaling pathways in the midgut and Malpighian tubules, and the locomotion behavior of P. helleri workers. The estimated lethal concentration (LC₅₀) of thiodicarb for P. helleri was 87 μg a.i. mL⁻¹. Bees fed this concentration exhibited morphological damage to the midgut epithelium and Malpighian tubules, including brush border degeneration, increased cytoplasm vacuolation, and the release of cell fragments into the intestinal lumen. In the midgut, regenerative cells showed cytoplasm disorganization and nuclear pyknosis. Immunofluorescence analysis revealed an increase in cell death via autophagy and apoptosis in the epithelial cells of the affected organs. Ingestion of thiodicarb also altered the bees' locomotion, resulting in increased meandering and decreased walking speed and total distance traveled. These findings demonstrate that the LC₅₀ of thiodicarb causes damage to non-target organs as the midgut and Malpighian tubules, and impairs behavior, which may ultimately affect the pollination services provided by P. helleri. These results enhance our understanding of the vulnerability of stingless bees to insecticides and underscore the importance of strategies aimed at protecting these pollinators.