Here at Pine Hill, though, the work hasn't stopped. And I wanted to collate my last few months of research and reading on the effect chemical wormers have been found to have on dung beetle populations. I started this little side project when I realised I would absolutely need to worm my horses this autumn for bots, given the number of eggs I was seeing and trying to remove (and with over a dozen horses on the property, spending hours a day removing bot eggs just wasn't feasible!). The list of 'safe' wormers I had been given by the Landcare dung beetle group only mentioned cattle and sheep worming products so that was no help whatsoever.
I had wanted to undertake worming as needed using Fecal Egg Counting, however I realised there are significant problems with this approach. The first is that not all invasive worm species leave eggs in dung - bots are a good case in point. Second was that I would have to either send specimens off fairly regularly for examination, or drop a cool $500 or so on my own microscope (which I DO plan on doing when I can!). Lastly, it was a very troublesome and time-consuming task to identify manure from individual horses, grab it before the beetles did, wrap it in damp newspaper and a plastic bag, label it and stick it in the freezer. I wanted to have tests connected to individual horses rather than just herd samples so I could really target my worming program. Given that I work full-time and have two kids, this just wasn't working.
So, I began to research horse wormers. Here's what I found (all sources listed at the end):
The active ingredients in wormers used to be fairly simple and basic: ivermectin was by far the most common, and still forms the active ingredient in most wormers on the market - in one form or another. Ivermectin has since been formulated into more potent (and therefore lower doses can be used) compounds such as avermectin and abamectin, as well as eprinomectin (safe for dairy cows) and doramectin (produced less discomfort to the animal on administration). Ivermectin and related drugs are very toxic to dung beetles in Australia. From here on in, when I refer to 'ivermectin' I'm including all the variations listed above.
I focused on research conducted in Australia and other like countries with dry summers and cooler wetter winters (ie South Africa, parts of America, Spain etc) rather than UK studies or studies in tropical countries. It appears rain and humidity have a significant impact on the mortality/adverse effects of ivermectin etc on beetles. Studies showed that:
- As horses aren't ruminants (ie they don't digest their food to the same stage cows do, for example), they excrete their food much faster and don't breakdown/metabolise the wormer in their gut at the same rate. This means that horse dung contains much higher concentrations of toxins than cow manure and is therefore more toxic to dung beetles.
- Ivermectin significantly reduces dung beetle brood emergence and brood take roughly 2.5 times longer to emerge than normal. So, this slows the beetle breeding rate significantly.
- Ivermectin kills all the dung beetles ingesting treated dung for at least the first 24 hours post-worming and this mortality rate gradually reduces to no apparent effect on the beetles by day 6.
- Ivermectin-treated manure is actually really attractive to dung beetles for up to 30 days! So, if you treat one horse with ivermectin but the others in the paddock aren't treated, the dung beetles will prefer the treated dung and this obviously results in higher mortality.
- Specific species of dung beetle are more susceptible to ivermectin than others. For example, O. Binodis is highly sensitive - ivermectin is 100% lethal to Binodis for the first week and it takes over eight weeks for ivermectin to have no measurable effect on this beetle.
- The ecotoxilogical effects of ivermectin are much more severe in drought conditions.
- Abamectin/ivermectin remain in dung samples for up to 180 days. Abamectin is particularly nasty for dung beetles in any concentration at all. Similarly, eprinomectin is highly toxic to dung beetles, reducing the next generation by 25%-30%.
From this research I could ascertain that, if you must use ivermectin-based wormers:
- Keep your horse away from your pastures and pick up and bag all manure from that horse as quickly as you can, for at least the first couple of days and this will drastically reduce the effect on your dung beetle population.
- High rainfall appears to mitigate the detrimental effects on dung beetles - so if you are considering using an ivermectin-based wormer, wait til it's about to rain and this will help alleviate some of the toxicity to dung beetles.
However, there really isn't a safe way to use ivermectin and its variants in relation to dung beetles. Ivermectin stays around for over four months, though only abamectin, the most toxic variant to dung beetles, is still harmful by this time.
Why don't we just use wormers that don't contain ivermectin, I hear you ask? Well, there really aren't many that don't, and those that don't generally don't treat horses for all known worms, including bots. I have an annual worming program - ie I only worm all the horses once per year - in Autumn. There is really no way to get rid of bloody bots, so I must use a boticide. The usual 'dung-beetle safe' or 'rotational' wormers don't do bots too.
The main wormer I had used before was 'Strategy T', manufactured by Virbac, and containing oxfendazole and pyrantel as dual active ingredients. Oxfendazole appears to have no observable effect on dung beetles (yey!) and pyrantel is similarly benign for invertebrates but the thesis is that it may adversely effect your soil microbiome and potentially earthworms. Either way, it doesn't do bots, and this made it a bit useless for me.
With regard to boticides, there is one active compound mentioned in the research that seems to be less toxic to dung beetles. Moxidectin, at recommended dosage levels, appears to have little effect on dung beetles, particularly after 2 days. However, at higher levels this compound is problematic and it seems to be somewhat toxic to dung beetles for the first two days at least. This is one of the active ingredients in Equest Plus Tape, made by Zoetis.
The other active ingredient is praziquantel. This is non-lethal and appears non-toxic for dung beetles. I could only find one study that tested praziquantel but it showed a definite lack of lethality until extremely high doses.
I receive absolutely no sponsorship from Zoetis (or, for that matter Virbac) and have no relationship with either company. I found the array of wormers on the market completely baffling and decided to sit down and do my own research to make sure any chemical wormer I'm giving my horses is as safe for my beloved beetles as possible. So, I'm giving Equest Plus Tape a go for this round and will closely monitor my beetle populations.
I have just discovered our very first B. bison, a wintering beetle. This means we finally have dung beetles working on our property all year round! The bison is a great beetle, burying its brood in balls of manure 20-40cm below the dung. This is some deep soil conditioning going on all winter long. Love it. However, this is also worrying if I'm using a chemical wormer that may have an adverse impact on those beetles. I think at this point it's a matter of weighing up your options and just doing the best we can!
I have just discovered our very first B. bison, a wintering beetle. This means we finally have dung beetles working on our property all year round! The bison is a great beetle, burying its brood in balls of manure 20-40cm below the dung. This is some deep soil conditioning going on all winter long. Love it. However, this is also worrying if I'm using a chemical wormer that may have an adverse impact on those beetles. I think at this point it's a matter of weighing up your options and just doing the best we can!
Please leave comments or questions and I'll do my best to answer them. Or just email me at pinehillpastoral@gmail.com.
References:
References:
Jacobs, C.T. & Scholtz, C.H., 2015, ‘A review on the effect of macrocyclic lactones on dung-dwelling insects: Toxicity of macrocyclic lactones to dung beetles’, Onderstepoort Journal of Veterinary Research 82(1), Art. #858, 8 pages. http://dx.doi.org/10.4102/ojvr.v82i1.858
Alexander, M. & Wardaugh, K., 2001, 'The Bardon Report' (Workshop on the Effects of Paraciticides on Dung Beetles', CSIRO Entomology Technical Report No. 89
Hempel, H. et al, 2006, 'Toxicity of four veterinary parasiticides on larvae of the dung beetle Aphodius Constans in the laboratory' Environmental Toxicology and Chemistry, Vol. 25, No. 12 pp 3155-3163
Alexander, M. & Wardaugh, K., 2001, 'The Bardon Report' (Workshop on the Effects of Paraciticides on Dung Beetles', CSIRO Entomology Technical Report No. 89
Hempel, H. et al, 2006, 'Toxicity of four veterinary parasiticides on larvae of the dung beetle Aphodius Constans in the laboratory' Environmental Toxicology and Chemistry, Vol. 25, No. 12 pp 3155-3163
