Thermal physiology of dung beetles exposed to ivermectin, a veterinary drug

Abstract

Global changes, including increasing temperatures and pesticide contamination threaten insect survival and reproduction by altering metabolism and stress responses. Of particular importance are insects that provide ecosystem services and are threatened by multiple stressors, such as dung beetles, which bury dung in forests and cattle pastures. This study investigated how elevated temperature and ivermectin, a common antiparasitic medication used in cattle that is excreted in dung, affect the thermal physiology of Euoniticellus intermedius dung beetles under controlled laboratory conditions. Our study evaluated, under laboratory conditions, the effect of the combination of high temperature and ivermectin, on heat tolerance, metabolic rate, and survival of female dung beetles E. intermedius. We found that ivermectin reduced survival at 29 °C but not at 33 °C, potentially due to heat-induced hormetic effects, which activate defense systems, protecting organisms from the effects of a second stressor, in this case, ivermectin. Ivermectin and high temperature increased metabolic rate, which could have potential negative effects on oxidative stress and longevity. Finally, critical thermal maximum was not affected by ivermectin or temperature. By impacting physiological traits and individual survival, high temperatures and pesticides may disrupt population dynamics and ecosystem services provided by dung beetles.