Effects of the veterinary anthelmintic moxidectin on dung beetle survival and ecosystem functioning

Macrocyclic lactones (MLs) are a class of chemical compounds administered to livestock for parasite control. These compounds are poorly metabolized and are predominately excreted in dung. When coprophagous insects such as dung beetles (Coleoptera: Scarabaeoidea) are exposed to ML residues, lethal and sublethal effects are often observed. Indirectly this can lead to ML residues impairing ecosystem functions that underpin production. A strategy to reduce these negative effects involves selecting 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 and functioning (short- and long-term estimates of dung removal). When exposed to moxidectin, adults of the sensitive species (Geotrupes spiniger Marsham) experienced a 43% reduction in survival. In contrast, survival of the non-sensitive species (Aphodius rufipes L.) was unaffected. We found little evidence to suggest moxidectin impaired dung removal. We found however, that high densities of a species with relatively low functional importance (A. rufipes) can compensate for the loss of a functionally dominant species (G. spiniger). Over a longer timeframe, earthworms fully decomposed dung irrespective of moxidectin residues.