Analysing the effect of ivermectin on the volatile organic compounds of dung and its possible influence on attraction to dung beetles

Dung odours are composed of a large number of different volatile organic compounds (VOCs). Dung beetles are attracted to dung by olfactory cues, and their selection depends on the odorous VOCs emitted from this resource. The possible effects of ivermectin (IVM) on the chemical composition of dung volatile emissions and how this could modify its attraction to dung beetles have been debated for years.In this work, we analysed the possible effects of IVM on the VOCs emitted by cattle dung and the attraction of the dung beetle Ateuchetus cicatricosus Lucas, using behavioural bioassays.The results of the study showed that the chemical analyses of the dung volatile emissions from untreated cattle, treated cattle with IVM (200 mu g/kg b.w.; collected at 7 and 14 days post-administration) and dung spiked with IVM (100 and 500 mu g/kg) were not significantly different. We detected a total of 44 VOCs among the treatments. The olfactometer bioassays showed no significant difference in the rates of attraction between different treatments.This study suggests that cattle dung does not experiment with a direct modification of the volatile compounds emitted, either via the digestive tract of cattle or by direct addition with IVM, ruling out the possible influence of any transformation product from the anthelmintic that could be present. In addition, a change in the microbiota of the digestive tract in cattle as a result of the mode of action of the drug is not supported. Further possible indirect effects are discussed. Ivermectin (IVM), either applied to the cattle or spiked directly into cow dung, does not produce a significant qualitative difference in the emission of their volatile organic compounds (VOCs).When the treatments were tested with the dung beetle Ateuchetus cicatricosus (Lucas, 1846) through olfactometer bioassays, there were no significant differences in the rate of individuals attracted.Though previous hypotheses for a direct effect of IVM in the alteration of the VOCs of cattle dung are not supported by our results, further possible indirect effects are discussed.image