John Wiley & Sons, Ltd.

A field test of the effect of spiked ivermectin concentrations on the biodiversity of coprophagous dung insects in Switzerland

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Veterinary medical product residues can cause severe damage in the dung ecosystem. Depending on the manner of application and the time after treatment, the excreted concentration of a given pharmaceutical varies. The popular anthelmintic drug ivermectin (IVM) can be applied to livestock in several different ways and is faecally excreted over a period of days to months after application. In a field experiment replicated in summer and autumn, we mixed six IVM concentrations plus a null control into fresh cow dung to assess the reaction of the dung insect community. Taxon richness of the insect dung fauna emerging from the dung, but not Hill diversity 1D or the total number of individuals (abundance), decreased as IVM concentration increased. Corresponding declines in the number of emerging insects were found for the majority of larger brachyceran flies and hymenopteran parasitoids, but not for most smaller nematoceran flies or beetles (except Hydrophilidae). Parallel pitfall traps recovered all major dung organism groups that emerged from the experimental dung, though at times in vastly different numbers. IVM generally did not change the attractiveness of dung: differences in emergence therefore reflect differences in survival of coprophagous offspring of colonizing insects. As our sample size was limited to six replicates, we generally recommend >10 (seasonal) replicates and also testing higher concentrations than used here as positive controls in future studies. Our results accord with parallel experiments where the substance was applied and passed through the cow's digestive system. In principle, therefore, our experimental design is suitable for such higher tier field tests of the response of the entire dung community to pharmaceutical residues, at least for IVM. This article is protected by copyright. All rights reserved

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