Ivermectin causes adverse effects on the metabolic rate and thermoregulatory capacity of Dung beetles

Ivermectin (IVM), a commonly used endectocide in livestock, has been shown to produce adverse effects in dung beetle ecology, physiology, reproduction, and even their ecosystem services. However, the ever-growing ecological importance of thermoregulation and its associated metabolic demand in dung beetles has not received as much focus regarding the effects of this drug. Here, we evaluated experimentally the effects caused by IVM in the metabolic rate and thermoregulation of Ateuchetus cicatricosus (Lucas, 1846), using a standardized ecotoxicity test based on thermolimit respirometry combined with infrared thermography (TLR-IR). The total capacity of excess heat regulation (iTR) and the caloric metabolic rate (MR) gave the most sensitive responses to IVM ingestion. The inhibition concentration at 50% (IC₅₀), a relevant toxicity threshold used to calculate the concentration of IVM that provokes a response half way among the inhibition responses obtained showed that iTR was impacted at 0.39 µg g^-1, while the MR was compromised at 0.24 µg g^-1. Applying a TLR-IR procedure has not only revealed how the MR of active thermoregulators is crucial for their adaptation in warm and competitive environments, but also shown the potential of this method to be applied in real-world scenarios like cattle-farming regions, where the need to assess the direct impact of endectocides like IVM is vital to update and enhance regulation guidelines of these pharmaceuticals.