Effects of ivermectin on soil nutrient cycling, plant biomass, and dung beetle abundance

Ivermectin, a commonly used parasiticide, is known to affect dung beetle abundance when present in cattle dung. In this experimental study, we explicitly manipulated ivermectin concentrations in dung pats to examine its effects on dung beetle abundance, soil properties, and plant growth throughout the growing seasons of spring and summer in a western South Dakota grassland. Dung pats containing zero, low (2 mg/kg), and high (10 mg/kg) concentrations of ivermectin were strategically placed in the grassland in summer 2019 and spring 2021. Over a period of 63 days, we monitored changes in the nitrogen content of dung, soil, plants, as well as the abundance of dung beetles, and plant biomass. Our findings indicated that beetle abundance was 50% greater in dung pats without ivermectin, especially when the dung was fresh. However, ivermectin concentrations did not significantly alter the nitrogen content in dung and plants across both seasons, nor was there a discernible effect on plant biomass, despite the pronounced impact on dung beetle abundance.