Effects of the veterinary anthelmintic moxidectin on dung beetle survival and dung removal

Macrocyclic lactones (MLs) are chemical compounds administered to livestock for parasite control. These compounds are poorly metabolized and pass relatively unchanged into the dung of treated animals. When coprophagous insects such as dung beetles (Coleoptera: Scarabaeoidea) are exposed to ML residues while feeding on dung, lethal and sublethal effects are often observed. This can lead to ML residues impairing ecosystem functions that underpin agricultural production. A strategy to reduce these negative effects involves the use of compounds that offer lower risk to non-target invertebrates, such as the ML moxidectin. Considering two dung beetle species with differing sensitivities to agricultural intensification, we asked whether exposure to moxidectin residues influenced survival, reproductive output, and functioning (short- and long-term estimates of dung removal). When exposed to moxidectin, adults of the sensitive species - Geotrupes spiniger Marsham (Scarabaeidae) - experienced a 43% reduction in survival. In contrast, survival of the non-sensitive species - Aphodius rufipes L. (Scarabaeidae) - was unaffected. We were unable to determine whether exposure affected reproductive output of either species. We found little evidence to suggest moxidectin impaired dung removal. However, high densities of a species with relatively low individual functional importance (A. rufipes) can compensate for the loss of a functionally dominant species (G. spiniger). Over a longer time frame, earthworms decomposed dung fully, irrespective of moxidectin residues. This functional redundancy reinforces that wider justification for the conservation of biodiversity should remain integrated into agricultural policy and practice.