Dr Nick Waipara explores the biosecurity issues of introducing exotic dung beetles onto organic farms in New Zealand.
Recent months have seen the first of a series of releases of exotic dung beetles on New Zealand farms. Organic farmers potentially have much to gain from dung beetles, but may also be vulnerable should dung beetle introductions have unwelcome side-effects. So, should organic farmers (and the rest of us) be concerned about new dung beetle introductions, and if so, why?
Well, here in the biosecurity team at Auckland Council, we are not anti-dung beetle. In fact Auckland Council Biosecurity co-funded the initial investigation into the feasibility of dung beetle release in New Zealand. We see the potential value in dung beetles as a chemical-free tool with a range of potential benefits. And it is quite possible, maybe even probable, that introducing new species of dung beetles may have no serious negative impacts. However, once we introduce a new organism, it is very difficult, if not impossible, to get rid of it if we change our minds. Therefore, ‘probably safe’ isn’t good enough. As advocated within public discussions over genetic engineering, a precautionary approach is essential, and new introductions should be preceded by sound scientific assessment of the risks and benefits.
The Dung Beetle Release Strategy Group (DBRSG) argues sound risk assessment has occurred through the then Environmental Risk Management Authority (ERMA – now the EPA) and subsequent research commissioned by the DBRSG. However there is far from consensus on this within the scientific community, with concerns raised by high profile scientists. Are these scientists in the pocket of Big Agribusiness? (Yes, I have been asked this!). No, they’re not; they genuinely believe questions remain unanswered regarding risks (and benefits) of dung beetle introductions, and these questions should be answered before, not after, introductions take place. Auckland Council agrees with these concerns.
Dung beetle proponents argue that when we imported sheep/cattle farming to New Zealand, we only brought part of an ecosystem. The logical solution, proponents argue, is to import the missing ecosystem component – exotic dung beetles. This same argument was applied to the problem of rabbits over 100 years ago. The solution on that occasion was to introduce stoats – a salutary reminder that, used simplistically, this logic may be superficially appealing but can get us into trouble.
The same logic does underpin the wider science of biological control, and has merit when used with caution. Biocontrol has successfully controlled many weed and pest species. However the more we learn about biocontrol, the more we understand that introducing any new organism will almost always affect more than just the pest it was introduced to control. In many cases, non-target effects are subtle, complex and difficult to detect. Equally, in most cases benefits clearly outweigh non-target effects. However it is important that prior to introduction we have good information on both the benefits and likely risks in order to make informed choices on which species to introduce and which to reject.
Which brings us back to dung beetles – do we know enough about the potential risks and benefits? Some concerns originally raised by Auckland Council and the science community have been addressed by subsequent research. This has created the undesirable scenario of attempting to demonstrate the safety of an organism after it has already been approved for release. However questions remain over issues as diverse as potential dung beetle effects on human and livestock disease transmission, livestock parasitology, greenhouse gas emissions from dung, potential to facilitate other invasive species such as possums and rats, and ability to colonise native forest remnants and alter native decomposer communities. Many of these issues have been addressed superficially by recent research or reviews commissioned by the DBRSG, but this has been insufficient to satisfy concerns of peer reviewers from universities and Crown Research Institutes.
Peer review suggests that provisional results are reassuring but do not address all concerns, and some results to date are of questionable rigour due to methodological flaws, reliance on questionable assumptions, and limited real-world applicability. Successful dung beetle programmes overseas are cited as evidence of safety, but in many cases there has been little of the follow-up monitoring required to detect negative effects if they were occurring. In Australia introduced dung beetles facilitate invasive cane toads – a link only identified within the last couple of years, decades after dung beetle introductions began in Australia.
And what about the benefits? Dung beetles can bury dung spectacularly fast, with accompanying benefits including fly and nematode control and increased pasture growth. In such cases, farmers are understandably happy with the results. However international research shows that these results are variable across different dung beetle species, seasons and environments. Promising results in laboratory studies are not always detectable in on-farm studies. Closer to home, DBRSG trials have shown some promising results. But again, peer reviewers have found these benefits to have been overstated, and queried their real-world applicability.
Many questions remain, but the financial cost of the science required to do justice to these questions is not insignificant. Dung beetle enthusiasts and sceptics alike are currently faced with a challenging economic climate, where research funding is hard to come by. Does this excuse foregoing comprehensive science in favour of assuming things will be OK? Or should a precautionary approach and a high bar be applied to potentially irreversible species introductions?
The rules are extremely onerous for introduction of insects for classical biocontrol programmes – as they should be. These rules should similarly apply to dung beetles. I would also argue that while we may struggle to fund thorough science, we can equally ill afford to find out all too late that we got it wrong.
Dr Nick Waipara is principal advisor for biosecurity, Auckland Council, Te Kaunihera Tamaki Makaurau.
Eleven species approved
See the 11 new dung beetle species that the EPA has approved for release in New Zealand at: