Dung beetles reduce livestock gastrointestinal parasite availability on pasture.
Anthelmintics are widely used to control gastrointestinal parasites of livestock. However, the residues of these compounds, particularly the macrocyclic lactones, are excreted largely unmetabolised in faeces, where they may have toxic effects on dung-colonising insects. Impoverishment of the coprophagous beetle community impairs the process of dung recycling and, as a result, may enhance the persistence of dung-dwelling helminth parasitic stages. To test this possibility, a large-scale field trial was conducted in south-west England. The availability of infective parasite helminth larvae (L3) was investigated on the herbage around 240 artificial 1-kg dung pats that had been constructed from the faeces of beef cattle with naturally acquired strongyle infections. Herbage up to 15 cm surrounding each pat was sampled at 2, 4, 6, 8 and 10 weeks after deposition. Pats were subject to enhanced, natural or no dung beetle colonisation and uncontrolled or enhanced rainfall. Under uncontrolled rainfall conditions, 2 weeks after pat deposition, significantly more L3 were recovered from around pats that were exposed to beetle colonisation than from pats that were not colonised. However, by week 8, significantly fewer L3 were recovered from around pats that were exposed to beetle colonisation compared to uncolonised pats. Under conditions of enhanced rainfall, pats yielded significantly more L3 than under uncontrolled rainfall conditions, and there were no differences in recovery from herbage around pats with enhanced, natural or no beetle colonisation. The data suggest that over the duration of a summer grazing season, temperate habitat dung-colonising insect communities, which include mainly small endocoprid dung beetles of the genus Aphodius, can reduce the development and survival of livestock gastrointestinal parasites on pastures, but that this can be overridden by the effect of high rainfall. Synthesis and applications. The work demonstrates that conservation of dung beetle populations in temperate climates is important in livestock management, not only for their essential role in dung degradation and nutrient cycling, but because their activity can also reduce the survival and availability of gastrointestinal parasites on pastures.