Synergistic effects of elevated temperature with pesticides on reproduction, development and survival of dung beetles

Abstract In times of global change, high temperatures can potentiate the negative effects of pesticides and other stressors. Here, we evaluated under controlled laboratory conditions the effect of a moderate increase in temperature in combination with ivermectin (an antiparasitic drug used in cattle that is excreted in dung), an herbicide, and parasitic pressure, on the reproductive success, development time and adult survival of dung beetles Euoniticellus intermedius, which are naturally exposed to these stressors. We found that heat increased the number and proportion of emerged offspring, but in combination with ivermectin, herbicide and parasitic treatments, it had synergistic negative effects. Moreover, heat in combination with ivermectin and with parasitism caused a synergistic increase of adult offspring mortality and, in combination with the herbicide, heat synergistically accelerated development. Our results indicate that heat can enhance the negative effect of other stressors and act synergistically with them, harming dung beetles, a group with important ecological and economic value in natural and productive ecosystems. Although adult sex ratio was not affected by experimental treatments, contrasting responses were found between males and females, supporting the idea that both sexes use different physiological mechanisms to cope with the same environmental challenges. The effects that combined stressors have on insects deepen our understanding of why we are losing beneficial species and their functions in times of drastic environmental change.