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

Abstract

10 11 1. Macrocyclic lactones (MLs) are a class of chemical compounds administered to 12 livestock for parasite control. These compounds are poorly metabolized and are 13 predominately excreted in dung. 14 152. When coprophagous insects such as dung beetles (Coleoptera: Scarabaeoidea) are 16 exposed to ML residues, lethal and sublethal effects are often observed. Indirectly 17 this can lead to ML residues impairing ecosystem functions that underpin production. 18A strategy to reduce these negative effects involves selecting compounds that offer 19 lower risk to non-target invertebrates such as the ML moxidectin. 20 21 3. Considering two dung beetle species with differing sensitivities to agricultural 22 intensification, we asked whether exposure to moxidectin residues influenced 23 survival, reproductive output, and functioning (short-and long-term estimates of dung 24 removal).25 26 4. When exposed to moxidectin, adults of the sensitive species (Geotrupes spiniger 27 Marsham) experienced a 43% reduction in survival. In contrast, survival of the non-28 sensitive species (Aphodius rufipes L.) was unaffected. We were unable to determine 29 whether exposure affected reproductive output of either species.30 31 5. We found little evidence to suggest moxidectin impaired dung removal. We found 32 however, that high densities of a species with relatively low functional importance (A.33 rufipes) can compensate for the loss of a functionally dominant species (G. spiniger). 34 Over a longer timeframe, earthworms fully decomposed dung irrespective of 35 moxidectin residues.36