Simulated Targeted Anthelmintic Treatment Maintains Dung Removal but Not Dung-Inhabiting Insect Communities

The intensive use of antiparasitic treatments, such as macrocyclic lactones, is known to affect non-target dung-inhabiting insects, leading to reduced community functioning and ecosystem services. We describe the development of a spatially explicit simulation to assess the effects of the treatment of different proportions of a livestock herd with anthelmintics, a strategy known as targeted selective treatment. We simulated the treatment of a varying proportion of a livestock herd with antiparasitics, and the effects inflicted on three dung-inhabiting insect guilds (flies, endocoprids and paracoprids) with novel life cycle, colonisation and dispersal mechanisms. We varied livestock stocking density to test the effect of dung availability on these effects. Complex population-level effects were seen as treatment varied, while increased stocking densities led to smaller community sizes overall. Dung removal, measured by total pat number and mean pat biomass, increased with decreasing livestock treatment at all stocking densities. These findings provide a theoretical basis for promoting targeted selective treatment with antiparasitics in an effort to balance livestock production and animal welfare with biodiversity and ecosystem functioning.