Dung roaming: a controversial approach to cleaning up New Zealand's cattle waste

Although I've already discussed the dangers of using biological control in various countries, a couple of recent events suggested I should write an update that concentrates on one particular example in New Zealand. I've mentioned elsewhere that my local reserve in Auckland is home to a large number of non-native species, from Australian eucalyptus trees and the associated (but accidentally imported) Emperor Gum moth, to California quail and Mexican gambusia fish. But having seen rainbow skink in my local environs, including a neighbour's garden, I was surprised to learn last week they are not native but yet another unplanned Australian import. Sure enough, the 1947 classic Powell's Native Animals of New Zealand makes no mention of the species in the page on the indigenous common skink and copper skink.

Earlier this year I read Quinn Berentson's superb Moa: the life and death of New Zealand's legendary bird, which lists fifty-eight avian species as having become extinct since humans first arrived in the country less than a thousand years ago. And of course this decimation of native fauna and flora may not yet have ended, with NIWA for example fighting a rear guard action against unwanted marine incomers such as polychaete worms arriving on ship's hulls and in discharged ballast water. Various sources suggest that well over one hundred introduced species of land animals, birds and fish are now widespread in New Zealand: what chance does the native ecosystem stand against this onslaught?

To add insult to injury, I recently read an OECD chart delineating business spend on research and development as a percentage of GDP, and was shocked to find that New Zealand was fourth from bottom of twenty-six nations, coming below western Europe, South Korea, Japan, Australia, Canada and the USA. Are our captains of industry really so short-sighted? As a country that depends extremely heavily on its dairy industry - an industry that is currently in dire straits - it seems sensible to invest a large amount of R&D in this sector. But alongside the eco-friendly solutions such as minimising methane emissions, there has been a new programme of biological control aimed at one particular side effect of dairy farming, namely the enormous amounts of cattle dung produced.

Across the Tasman, Australia has already been working on a similar scheme for the past half century, deliberately introducing numerous species of non-native dung beetles. New Zealand, home to over ten million cattle in a 3:2 dairy-to-meat ratio, obviously has issues with bovine manure management. Due to the lack of native ruminants the country's fifteen indigenous dung beetle species have evolved to mostly inhabit forests rather than grazing land.

There are various reasons why speeding up the rate of dung decomposition would improve farm land and the landscape in general, from preventing mineral imbalance in the soil and contamination of waterways to reduction in animal-infesting parasites such as nematode worms. But is it worth the risk to the greater environment, considering the dismal track record of biological control schemes around the world?

The new project is not the first time such insects have arrived in the country: in addition to three species accidentally imported from Australia and South Africa from the late Nineteenth Century onwards, the Mexican dung beetle (Copris incertus) was deliberately introduced into three areas in the 1950s but only thrived in the warm Northland climate. It is the scale of the new research that has set it apart: following caged field trials, the past two years has seen the widespread introduction of eleven non-native species across seven regions on both North and South Islands.

Bodies such as the Institute of Environmental Science and Research (ESR) have investigated the potential dangers to human health and the local ecology, even testing if possums, carriers of bovine tuberculosis, might see the exotic insects as a new food source. Even so, some professional scientists have deemed it a biosecurity disaster and one can see their point: using data from other countries' programmes is hardly a fool-proof comparison, considering the profoundly different indigenous ecosystems of Australia and New Zealand.

As a child I heard about the food chain or pyramid, but this is something of a misnomer. Just as natural selection works with bushes rather than linear progression, so there are food webs consisting of a complex series of trophic interactions. Although exotic dung beetles are unlikely to displace their native counterparts due to lack of shared environments, it is possible that other native species of grassland-living insects could suffer, such as humble earthworms. The problem is that without testing in various regions over long periods of time, it isn't viable to rule out such side consequences. Yet it isn't possible to undertake such tests without release into the wild: do we have something of a catch-22?

Having said that, there are no obvious signs that Australia's long-established dung beetle programme has had anything like the deleterious effects of its other biological control schemes, such as the cane toad fiasco. But then fifty years is a very short time in ecological timeframes and what to the casual glance of a farmer appears to be equilibrium could be apocalyptic at dung beetle scale. I wish the project good luck, but cannot help feeling that having received far more than its fair share of obnoxious aliens, New Zealand is the last place that needs yet more exotic species introduced onto its green and pleasant land.

Predators vs poisons: the ups and downs of biological control

Ever since Darwin, islands and island groups have been known as prominent natural laboratories of evolution. Their isolation leads to radiation of species from a single common ancestor, the finches and giant tortoises of the Galapagos Islands providing a classic example. But a small population restricted in range also means that many island species are extremely susceptible to external factors, rapid extinction being the ultimate result - as can be seen from the dodo onwards. Living as I do on an island (New Zealand counts within the terms of this discussion, as I will explain) has led me to explore what a foreign invasion can do to a local population.

Either through direct hunting or the actions of imported Polynesian dogs and rats, almost half the native vertebrate fauna was wiped out within a few centuries of humans arriving in New Zealand; so much for the myth of pre-technological tribes living in ecological harmony! But the deliberate introduction of a new species to pray on another is now a much-practised and scientifically-supported technique. One of the late Stephen Jay Gould's most moving essays concerned the plight of the Partula genus of snails on the Society Islands of Polynesia. The story starts with the introduction of edible Achatina snails to the islands as food, only for some to escape and become an agricultural pest. In 1977 the Euglandina cannibal wolfsnail was brought in as a method of biological control, the idea being that they would eat the crop munchers. Unfortunately, the latest wave of immigrant gastropods ignored the Achatina and went after the local species instead. The results were devastating: in little more than a decade, many species of Partula had become extinct in their native habitat.

(As an interesting aside, the hero of Gould's Partula vs. Euglandina story is gastropod biologist Henry Crampton, whose half century of research into the genus is presumably no longer relevant in light of the decimation of many species. Yet Crampton, born in 1875, worked in typical Victorian quantitative fashion and during a single field trip managed to collect 116,000 specimens from just a single island, Moorea. I have no idea how many individual snails existed at the time, but to me this enormous number removed from breeding population in the name of scientific research was unlikely to do anything for the genus. I wonder whether comparable numbers of organisms are still being collected by researchers today: somehow I doubt it!)

The Society Islands is not the only place where the deliberate introduction of Euglandina has led to the unintended devastation of indigenous snail species: Hawaii and its native Achatinella and Bermuda's Poecilozonites have suffered a similar fate to Partula. Gould used the example of the Partula as a passionate plea (invoking 'genocide' and 'wholesale slaughter') to prevent further inept biological control programmes, but do these examples justify banning the method in totality?

The impetus for this post came from a recent visit to my local wetlands reserve, when my daughters played junior field biologists and netted small fish in order to examine them in a portable environment container (alright, a jam jar) - before of course returning them to the stream alive. The main fish species they caught was Gambusia, which originates from the Gulf of Mexico but was introduced to New Zealand in the 1930s as a predator of mosquito larvae. However, akin to Euglandina it has had a severe impact on many other fish species and is now rightly considered a pest. In fact, it's even illegal to keep them in a home aquarium, presumably just in case you accidentally aid their dispersion. Australia has also tried introducing Gambusia to control the mosquito population, but there is little data to show it works there either. The latter nation also provides a good illustration of environmental degradation via second- and third-hand problems originating from deliberate introduction. For example, the cane toad was imported to control several previously introduced beetle species but instead rapidly decimated native fauna, including amphibians and reptiles further up the food chain, via toad-vectored diseases.

Gambusia affinis: a big problem in a small fish

This isn't to say that there haven't been major successes with the technique. An early example concerns a small insect called the cottony cushion scale, which began to have a major impact on citrus farming in late Nineteenth Century California. It was brought under control by the introduction of several Australian fly and beetle species and without any obvious collateral damage, as the military might phrase it. But considering the extinction history of New Zealand since humans arrived, I've been amazed to discover just how many organisms have been deliberately introduced as part of biological control schemes, many in the past quarter century. For instance, twenty-one insect and mite species have been brought over to stem the unrestrained growth of weeds such as ragwort and gorse, although the rates of success have been extremely mixed (Old man's beard proving a complete failure, for example). As for controlling unwelcome fauna in New Zealand, a recent promising research programme involves the modification of parasites that could inhibit possum fertility. This is something of a necessity considering possums (first imported from Australia in the 1830s and now numbering around sixty million) are prominent bovine tuberculosis vectors.

Stephen Jay Gould was a well-known promoter of the importance of contingency within evolution, and how a re-run of any specific branch of life would only lead to a different outcome. So the question has to be asked, how do biologists test the effect of outsider species on an ecosystem (i.e. within laboratory conditions) when only time will show whether the outcome is as intended? No amount of research will show whether an unknown factor might, at an unspecified time during or after the eradication programme, have a negative impact. It could have been argued in the past that the relative cheapness of biological control compared to alternatives such as poison or chemicals made it the preferable option. However, I imagine the initial costs, involving lengthy testing cycles, mean that it is no longer a cut price alternative.

Considering the recent developments in genetic modification (GM), I wonder whether researchers have been looking into ways of minimising unforeseen dangers? For example, what about the possibility of tailoring the lifespan of the control organism? In other words, once the original invasive species has been eliminated, the predator would also rapidly die out (perhaps by something as simple as being unable to switch to an alternative food source, of which there are already many examples in nature). Or does that sound too much like the replicant-designing Dr Eldon Tyrell in Blade Runner?

One promising recent use of GM organisms as a biological control method has been part of the fight to eradicate disease-carrying (female) mosquitos. Any female offspring of the genetically altered male mosquitos are incapable of flight and thus are unable to infect humans or indeed reproduce. However, following extremely positive cage-based testing in Mexico, researchers appear to have got carried away with their achievements and before you could say 'peer review' they conducted assessments directly in the wild in Malaysia, where I assume there is little GM regulation or public consultation. Therefore test results from one location were extrapolated to another with a very different biota, without regard for knock-on effects such as what unwelcome species might come out of the woodwork to fill the gap in the ecosystem. When stakes are so high, the sheer audacity of the scientists involved appears breathtaking. Like Dr Tyrell, we play god at our peril; let us hope we don't come to an equally sticky end at the hands of our creation...