Toxicidade, efeitos comportamentais e fisiológicos da exposição ao neonicotinóide tiametoxam na vespa eusocial Polybia paulista (Ihering, 1896) (Hymenoptera, Vespidae)

Abstract

Neonicotinoids are among the most widely used insecticides to combat insects considered agricultural pests, however studies point out that exposure to these insecticides affects non-target organisms both at the individual level, with behavioral and physiological changes, and at the colonial level in the case of social insects. Despite evidence of the detrimental effects of neonicotinoid exposure on honeybees, the consequences to social wasps lack studies. Social wasps have great importance ecologically and economically as predators of a wide range of other insects, many of them considered agricultural pests, and they also consume floral resources such as nectar and are therefore susceptible to exposure in this process. In this study, we investigated the effects arising from exposure to the neonicotinoid insecticide thiamethoxam on the social wasp Polybia paulista. First, we developed a maintenance protocol for the wasps in the laboratory and by acute exposure we obtained the topical and oral lethal dose (LD50). From these doses, we evaluated the effects of acute exposure to sublethal doses on the locomotion behavior of foraging workers. Subsequently, we obtained the mean lethal concentration (LC50) and from this concentration we performed experiments to evaluate the mean lethal time (LT50) of workers when exposed to sublethal concentrations. To evaluate the consequences of chronic exposure to such concentrations, we conducted video recordings and analyzed the wasps' locomotion at different exposure times. We also conducted morphohistological analyses to evaluate the consequences of chronic exposure on the wasps' midgut and brain. Acutely exposed wasps showed an oral LD50 of 0.4870 and 0.4456 ng i.a./wasp (24 and 48h) and a topical LD50 of 1.0030 and 0.8246 ng i.a./wasp (24 and 48h). Wasps exposed to sublethal doses acutely had their mobility impaired. The LC50 obtained after 24 h was 0.235 ng i.a./ µL, wasps exposed to sublethal concentrations survived less and moved significantly less than unexposed wasps, regardless of the exposure time tested. This result was also observed in morphohistological analyses of the brain and midgut. Our results demonstrate that P. paulista is as sensitive as other non-target species to thiamethoxam exposure, and that exposure to sublethal doses and concentrations significantly decreases survival as well as worker locomotion and causes morphohistological damage to foraging P. paulista. We conclude that social wasps may be as susceptible as other non-target insects to neonicotinoid exposure, with their behavior and organs impaired as a result of exposure.