This article has been modified from a University of Sussex press release with permission.
Domhnall Finch and Fiona Mathews, from the University of Sussex with collaborators from the Vincent Wildlife Trust and Agriculture and Agri-Food Canada, recently published a meta-analysis evaluating the “Implications of endectocide residues on the survival of aphodine dung beetles” in the SETAC journal Environmental Toxicology and Chemistry.
Ranchers and farmers across the world often use antiparasitic drugs to protect cattle and sheep from parasites. These drugs affect the ecosystem in a variety of ways, and therefore, their wide use is being scrutinized by regulatory authorities and environmental protection advocates.
Some endectocides, a class of antiparasitic drugs used to control nematodes and arthropods (such as ticks), are poorly metabolized by the gut of livestock and are thus excreted in dung. These products can linger in the environment and impact both flora and fauna in an ecosystem. They have been shown to impact dung beetles, which provide important ecosystem services for farmers. By ensuring that dung is cleared from pasture quickly, the beetles help to control pest flies and also allow for rapid grass regrowth through nutrient cycling, soil aeration and dung removal. In the UK alone, these services are estimated to exceed £350M per year. Moreover, dung beetles are vital prey items for a range of bat and bird species.
Fiona Mathews, Professor of Environmental Biology at University of Sussex noted that when compared with controls, dung samples from cattle treated with antiparasitic products had about a third fewer dung beetle larvae. Mathews said, “What’s particularly worrying is that the beetles actually seemed to be more attracted to treated dung but, because of the toxicity of the chemicals, their larvae have poor survival rates and face impaired development.” Over time, this reduces the number of dung beetles, which is troubling news for a range of bird and bat species, many already vulnerable, that are reliant on dung beetles for prey.
Finch and Mathews found that pour-on treatments — the most common form of application — was particularly damaging to dung beetle larvae. Their study also revealed that one of the most widely used anti-parasitic products, the agent Ivermectin, is extremely toxic; and none of the newer replacement agents had sufficient evidence to conclude that they were environmentally safe. The researchers stress that more research is needed into antiparasitic drugs treatment types other than pour-on treatments as well as newer drug formulations.
It is also worth noting that these products can be bought over the counter without the involvement of a veterinarian. There is already concern about over-use leading to the evolution of drug-resistant parasites, and this study provides additional evidence that their use should be more strictly controlled – ideally, being used under veterinary supervision.
The results of this research are particularly timely as they come just a few months after the UK government announced that it would not be funding extensions to higher-tier organic stewardship agreements in England. This means that farms that currently avoid the use of insecticides will be faced with a difficult choice moving forward because according to Mathews, “sticking to an insecticide-free approach may not be economically attractive compared with switching to conventional systems where the routine use of anti-parasitic agents is normal.”