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, reproductive output, 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 were unable to determine whether exposure affected reproductive output of either species. 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.