Effects of short term exposure to ivermectin on dung beetles' heat tolerance

Ivermectin ranks highest on the list of popular anthelmintics used in Sub-Saharan Africa due to its efficacy for gastrointestinal parasites. However, it is poorly metabolised and highly persistent such that most of the active ingredient is excreted unchanged in animal dung and urine from treated animals. This is reported to negatively affect coprophagic species, including dung beetles that feed and brood on mammalian dung. In arid tropical climate hotspots, these dung beetles, and their essential dung removal ecosystem services are already threatened by climate change related stress. However, how these two stresses interact and the effects on dung beetle fitness is unknown. Here, we investigated how short-term exposure to an ivermectin-laced dung diet affects dung beetle thermal responses in three dung beetle species vis paracoprids Copris elphenor, Digitophagus sahelicus and Geotrupe spiniger Using concentrations of 0.1%, 0.01%, 0.001% and 0.0001%, dung beetles were fasted for 24hours, before being fed on ivermectin diets for 48-hour continuously and subsequently measuring critical thermal maxima (CTmax). Preliminary results showed that exposure to ivermectin significantly reduced the beetles’ CTmax (p<0.001) by an average of 3.5% for C. elphenor, 4.46% for D. sahelicus and 7.99% for G. spiniger compared to controls. Digitophagus sahelicus was more tolerant to high temperatures (CTmax 45.15oC ±1.82) at the highest ivermectin residue concentration (0.1%) than C. elphenor, and G. spiniger. The study highlights the potential risk of parasiticides on dung beetles’ fitness and potentially population dynamics and ecosystem service provision.