First published by RSPB Centre for Conservation Science

Adverse effects of routine bovine health treatments containing triclabendazole and synthetic pyrethroids on the abundance of dipteran larvae in bovine faeces. 2019. Gilbert, G., MacGillivray, F.S., Robertson, H.L. & Jonsson, N.N. Scientific Reports. DOI: 10.1038/s41598-019-40800-6 VIEW

Recent media attention around the science which reviewed a massive decline in insect numbers across Europe and North America – suggests that, people do appreciate that this is a worrying trend, people are interested. Everybody can see why on some (if not every level) that insects are important.

Is it then not surprising that the regulations around testing the wider environmental effects of some pharmaceutical treatments of livestock seem ‘loose’ at best, when such veterinary pharmaceuticals may have direct impacts on a range of important insects, especially those associated with dung. Well that assumes we have cause to even think about it. On the surface, most of us really don’t tend to consider this sort of thing when we glance a nice field of sheep from the car, or tuck in to a juicy hamburger.

As a fairly seasoned conservation scientist with RSPB, a few years ago I did have cause to think about the relationship between livestock pharmaceutical treatments and their potential effects on insects and I was more than surprised at what we found in a paper published this week in Scientific Reports.

Red-billed Chough and insects
Working with RSPB colleagues on the beautiful island of Islay, in Argyll, Scotland, I was investigating the insect food available to the Red-billed Chough, a bird species in decline in Scotland and even at risk of disappearing from Scotland altogether. Although adapted to feeding mostly in soil, it is one of the few species which will regularly feed directly in dung, and on dung associated insects. One avenue of my research was to look at what may have caused a decline in the abundance of dung insects. My first thoughts on the likelihood of pharmaceutical treatments having caused any decline in dung insects in areas of Islay where Chough feed, were that this was extremely unlikely. I knew that there had some years before, been work by conservationists which highlighted the negative effects on dung insects of a parasiticide called Ivermectin, but that this was no longer used by farmers in areas where Chough breed and feed. The Chough is a very charismatic and well – loved bird by all the farming community and not using Ivermectin is just one of the measures taken by farmers on Islay to try to ensure that Chough will always be there.

Red-billed Chough is one of the few species that will regularly feed directly in dung, and on dung associated insects.

It quickly became clear that there were many other pharmaceutical treatments used as part of routine livestock welfare and management, but that these were considered to be environmentally ‘safe’ or at least there had never been any information or recommendations that these treatments might be harmful to dung insects, especially in a sensitive area such as Islay where there was already an awareness of the importance of this in connection to Chough and their food.

Not expecting to find any effects, we carried out some large field scale experiments to test a few of the most commonly used treatments. Being a scientist used to working on wild birds which don’t make it easy for us to study them, by either not being easy to find or by flying away – who knew? It was such a revelation to do some experimental science with stationary cow pats, that we rather went to town, and over two years carried out such large scale, robust experiments – the results of which were quite conclusive and difficult to ignore.

Two of the treatments we tested resulted in very significant reductions, in particular of fly larvae. This was true over both years and when the treatments were administered (as is usual) together, or separately. These are commonly used livestock pharmaceutical treatments which we would not have known had an effect on dung insects had we not tested them ourselves. Does this matter? Fewer maggots, fewer flies? Granted, these might not be the colourful, interesting insects that most people could learn to love, however fly larvae alongside other dung associated beetle larvae are potential chough food – but this result is important for several reasons. It does give us an avenue to explore by which we might be able to increase the availability of food to chough. It also gives us a big wake-up call that we are being naïve in our assumption that current regulations for testing veterinary pharmaceuticals are sufficient to provide suitable recommendations for their safe use where associated insects and wider wildlife are concerned.

It’s a bit scary to begin to project this one finding in a beautiful extensive pasture system on the Scottish Island of Islay – to the wider countryside. Those flies, beetles, worms, which we should learn to love because they have of course their own intrinsic value and their right to thrive; they are also food for a wide variety of species, moving up the food chain. Many UK bird species that feed on dung-associated insects, some of which may be soil based, have declined markedly in recent decades, including Lapwing, Curlew, Starling, Yellow wagtail, Swift, and Black -tailed Godwit. Well documented economically important services are provided by dung associated insects, such as dung degradation, cycling of nutrients into the soil and even reducing the spread of some parasitic diseases of livestock.

We hope that our dung detective work provides a robust piece of evidence that we need better testing of veterinary phamaceuticals, testing that is more relevant to routine practice and ecological processes. With so many unknowns, it is not possible to recommend practical solutions to quickly improve dung insect abundance. We need quality baseline science to provide the facts which allow informed decisions, and these need to be beneficial to the needs of livestock, farmers and wildlife.

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Image credits

Featured image: Red-billed Chough in flight | Ron Knight | CC BY 2.0 | Flickr
Middle: Red-billed Chough on ground | Dibyendu Ash | CC BY SA 3.0 |
Bottom: cow dung | Gillian Gilbert