Lasting decrease in functionality and richness: Effects of ivermectin use on dung beetle communities.
Intensification of agriculture has resulted in widespread use of antiparasitics, mostly macrocyclic lactones, which harms non-target organisms. Residues of such antiparasitics do primarily affect dung beetles, who provide keystone ecosystem services for pasture functioning
Intensification of agriculture has resulted in widespread use of antiparasitics, mostly macrocyclic lactones, which harms non-target organisms. Residues of such antiparasitics do primarily affect dung beetles, who provide keystone ecosystem services for pasture functioning, primarily the resource cycling via dung degradation, and to welfare of human and cattle alike, i.e., parasite control. Up to now, studies mainly focused on direct effects of ivermectin, the most widely used antiparasitic, while its long-lasting effects on routinely treated pastures have not yet been studied on real dung beetle communities and under field conditions. In addition, previous studies were usually conducted on limited amount of sites. We have therefore investigated both direct and long-lasting effects of ivermectin use on basic characteristics (species richness, abundance, biomass) and functionality (dung removal ability represented by guild composition) of dung beetle communities on multiple sites throughout the Czech Republic.
Ivermectin treated sites had ca. 35 % lower species richness and 44% lower abundance per pat. Per pat biomass did not change. However, from a functional perspective, ivermectin use significantly decreased the biomass of beetles with high contribution to dung removal (relocating and dwelling beetles), while the biomass of beetles with low contribution (dung visiting adults with saprophagous larvae) was not affected. This was accomplished with decrease in per pat functionality at treated sites, i.e., the dung removal ability of the community.
Our results highlight that the effects of ivermectin use can last far beyond its physical presence in the grazing system. Via its effects on dung beetles, routine antiparasitic treatment by ivermectin has negative consequences for both pasture biodiversity and ecosystem functioning (i.e., impaired nutrient cycling and parasite control), which in turn can have serious economic consequences.
We therefore advice three possible scenarios to lower the negative impact of antiparasitics use on dung beetle communities. Ideally, we suggest termination of antiparasitics use where possible, and returning to traditional practices, such as low intensity cross and rotational grazing. In cases, when the use of antiparasitics is necessary, we encourage using the alternative substances (e.g., benzimidazoles, pyrantel, praziquantel) with lesser or no impact on dung fauna instead of macrocyclic lactones (e.g., ivermectin). Finally, if the use of macrocyclic lactones is inevitable, we suggest more cautious approach to treating animals, thus lowering the effects of ivermectin on dung beetle communities (i.e., treating animals during the period in indoor stables, avoiding the temporal coincidence with high insect activity or treating only a fraction of herd at the time).
Ambrožová L., Sládeček F., Zítek T., Perlík M., Kozel P., Jirků M., Čížek L. (2021) Lasting decrease in functionality and richness: Effects of ivermectin use on dung beetle communities. Agriculture, Ecosystems and Environment 321 : article number: 107634.