17 July 2012

What to do with too much poo

Most Australians baulk at environmental solutions which involve exotic species, but the introduction of dung beetles has been a rare success story and now New Zealand is following suit.
Dung beetle

Scarabaeus viettei. Picture taken in western Madagascar. Credit: Wikipedia

The average cow will drop between 10 and 12 pads of about one litre of dung covering 0.82 square metres every day – and each one has the capacity to produce up to 3,000 flies within a fortnight.

Besides facilitating the excessive and unnatural abundance of bush flies in Australian farmland, large volumes of dung left unburied and unprocessed can remain for up to four years – its natural fertilisers locked up inside forever and wasted, or ending up in nearby waterways. Cattle will not graze near their own faeces, and accumulated dung can prevent the growth of vegetation, so large areas of dung-covered pasture can remain ungrazed for up to two years. Combined with the damage caused by large numbers of parasitic flies, this costs the cattle industry hundreds of millions of dollars every year.

The introduction of cattle to Australia with European settlement has brought with it the significant challenge of managing the accumulation of dung, because while we have around 400 species of native dung beetle, they are used to breaking down the dry, fibrous and pelletised droppings of marsupials such as kangaroos, wallabies and wombats. They can’t cope with the enormous volumes of dung produced by introduced livestock each day, so between 1969 and 1987, and again from 1990 to 1992, scientists from the national Australian science agency, the CSIRO, shipped in a range of exotic dung beetle species to address this problem. More recently, CSIRO scientists led by entomologists Jane Wright and Keith Wardhaugh, have introduced two species of European dung beetle to “finish the job”, according to a report released on the May 31 this year.

The idea of introducing dung beetle species from the origins of our livestock was first conceived by Hungarian entomologist and ecologist, George Bornemissza. Upon arriving in Australia from his native Hungary in 1951, Bornemissza remarked on how starkly different the cattle fields of Western Australia looked from the cattle fields back home. While the cattle fields of Hungary were clear and virtually dung-free, the cattle fields Bornemissza saw near a little town called Wooroloo were littered with scores of dried-up dung pads. So in 1965, Bornemissza led a team of scientists at the CSIRO in launching the Australian Dung Beetle Project, researching the particulars of species from 32 countries around the world, including their adaptive capacity to Australian climates, seasonal occurrence, rate of breeding, and dung collecting abilities. Since the establishment of this project, CSIRO has imported 43 species of dung beetle from Africa, Europe, Asia and North America, 23 of which have become established in their new environments.

Dung beetles belong to the superfamily Scarabaeoidea, which contains around 5,000 species and are often referred to as scarab beetles. They are found on all continents except Antarctica, and can live in a range of habitats, including desert, forest, farmland and grassland. Other organisms such as earthworms, ants and termites also have the ability to break down dung, but none can do it to quite the extent of the dung beetle – dung beetle larvae are able to consume up to 100% of their body weight of dung per day until pupation. Adult dung beetles will feed on what’s known as dung juice – or what postdoctoral research associate at the University of Nebraska-Lincoln, Sean Whipple, refers to as a “dung slurpie” in his thesis published in 2011 – which is primarily the moisture within the dung pad. This is because once they hit adulthood, the dung beetles develop filtering mouthparts that cannot bite through both moisture and fibre as the larvae’s biting mouthparts do. Dung is not only essential for dung beetle survival as a primary food source, the insects cannot reproduce without it, as it provides the materials needed to produce ‘brood balls’ into which eggs are laid and hatched.

Extensive research has been done on the environmental benefits brought by dung beetles, which includes cycling nutrients into the soil to create healthier pastures, reducing greenhouse gas emissions, and increasing soil aeration by tunneling, which lowers the runoff of surface wastes and the reduction of water contamination and algal blooms. In 2004, a thesis published by Matthew Bertone from the Department of Entomology at North Carolina State University in the U.S. found that by burying dung, dung beetles are having a positive impact on soil nutrients and pH and the growth of plant material, and in 1970, a study by Bornemissza and Williams found that dung beetles could almost double the yield of a Japanese cereal crop called millet.

Finding the right species of dung beetle to deal with cattle dung is only the beginning of the process, because introducing exotic species to a country as isolated as Australia is no small feat. It takes many years of offshore and onshore research to address the stipulations set out by the Quarantine Act and the Environment Protection and Biodiversity Conservation Act, which govern the bio-safety of new species introduced into Australia. This requires that negative environmental impacts be assessed, and an important part of this is to perform a host-specificity test, which determines which plant and animal species the proposed exotic species will eat. This ensures that an exotic species won’t wreak havoc on other species in its new environment.

If the tests meet all of the requirements, the Department of Sustainability, Environment, Water, Population and Communities will independently assess the risk, and make the decision to add the new species to the list of specimens suitable for import. Protocols are negotiated with the Department of Agriculture Fisheries and Forestry – Biosecurity for the introduction of the new species into Australian quarantine. “In our case, this means that only surface-sterilised dung beetle eggs can be released from quarantine,” says Wright. Then the beetles are mass-reared to produce sufficient numbers for release into the field.

“There is an established legislated process governing the bio-safety of new species introduced into Australia. This requires that negative environmental impacts be assessed,” says Patrick Gleeson from CSIRO Ecosystem Sciences, who was involved in the introduction of dung beetles this year. “In the case of dung beetles, Australia has considerable experience in importing these species and in assessing their impact. A key element of risk assessment is the consideration of what has happened in the past. Based on previous experience, there is no evidence of negative impacts on the environment which would preclude the importation of these species.”

“It was a very ambitious biocontrol programme and is now generally considered to have been a success,” says entomologist Marcus Byrne from the University of the Witwatersrand in South Africa, who worked on the Australian Dung Beetle programme from 1983 to 1986, but was not involved in the subsequent projects. “There have also been major ecological benefits in terms of nutrient cycling in the soil, water percolation into the soil and reductions in biting flies. Overall, I think it was a good thing. We cannot accept the ‘do nothing’ laissez-faire approach to the environment anymore. We are the custodians of the planet and therefore have to take steps to sort out the problems we have created, when we can.”

While the imported dung beetles proved a success, something the researchers needed to address was the seasonality of the introduced dung beetles. In the early 2000s, an informal group known as the Dung Beetles for Landcare Farming Committee was given funds by the Orica Community Foundation through Landcare Australia, and commissioned to evaluate the status of the introduced dung beetles. The resulting report by ex-CSIRO entomologist Penny Edwards, published in 2007, found that while Australia’s tropical and sub-tropical cattle grazing areas were being served by seven to 13 species of exotic dung beetles, the more temperate pastures were being tended by just four or five species. Of these, only one was active during the autumn to winter period, the rest waiting until spring to emerge before reaching a height of activity during summer. This behaviour represented a two to three-month gap in dung processing and burial, which saw the build-up of cattle dung and the return of the various negative environmental and agricultural effects associated with this, including access to dung for the spring influx of migrating bush flies (Musca vetustissima).

Edwards’ report reignited the search for suitable dung beetle species for importation, particularly species that were active during the autumn-to-winter period, and two perfect candidates were found in the south of France – Bubas bubalus and Onthophagus vacca. “In southern Australia, there is very little dung beetle activity in the late winter and early spring. This gap in activity allows dung to accumulate, leading to poor nutrient cycling and allows the increase in dung breeding pest flies populations. Using climate-matching software, B. bubalus and O. vacca … were chosen to be the most suitable candidates to fill the lack of beetle activity during this period,” says Gleeson. In early June, the CSIRO reported that the beetles had just produced their first eggs in the quarantine facility, which will be reared to adulthood and then released into cattle pastures.

The concept of deliberately introducing species has a tendency to make some Australians nervous, as it’s been almost 80 years since the cane toad was released in Queensland to deal with the native cane beetles (Dermolepida albohirtum), and we are yet to put a dent in their plague-like numbers. But this is an entirely different situation, according to Byrne. “The cane toad was introduced in 1935 to Australia … and the world was a very different place. The science of biological control was in its infancy and the introduction was utterly stupid,” says Byrne. “The short story can be described as lack of host specificity. The cane toad is a predator that eats anything that will fit in its mouth; it is also poisonous to anything that eats it. A good biocontrol agent is host specific, it can only live on one host – the target species, or in this case substance – cow dung. Dung beetles will not become pests in Australia.”

Andy Shepphard, an entomologist from the CSIRO Ecosystem Sciences and an expert in invasive species, agrees. “As these beetles can only persist in any numbers in the presence of the type of dung cattle produce (where would they find the dung they need to reproduce otherwise?), dung beetles will only be abundant in areas that have high levels of cattle grazing – that is, where the environment is primarily being altered by the grazing industry,” he says. “In commercially grazed ecosystems, any interactions the dung beetles may be having within this environment are likely to be extremely small compared to the impacts of the grazing livestock. Indeed, given that the beetles have already reduced the excessive and unnatural levels and abundance of bush flies in these environments, it would be easy to argue that the beetles have reduced the impacts these flies have had on human wellbeing and have led to a net environmental benefit.”

“We now have a rigorous process for assessing risk, which has proven itself an effective means of ensuring that no ‘new’ cane toad is introduced,” adds Gleeson. “There are always concerns about introductions that may have an adverse effect, and that is exactly the reason for having strict quarantine, testing and approval processes.”

In early 2011, Landcare scientists announced that they are in process of introducing 11 exotic species of dung beetle, including some Australian species, to New Zealand to address problems associated with cattle grazing.

“It was helpful that dung beetles are among the best studied of all the insects in the world. We can draw on the experiences of other countries, particularly Australia, where exotic dung beetles have been introduced, benefits achieved and risks found to be negligible. It was also helpful that there is a global community of dung beetle experts willing to provide information and advice,” says Landcare New Zealand research scientist Shaun Forgie.

But as with the Australian project, once the species are released, it will take many years before the scientists will know if the new species have become established and have had a positive effect on the environment. According to Gleeson, based on work with dung beetles in the past, they will probably have to wait for at least a decade. “The introduction of exotic dung beetles is not an instantaneous solution to the dung problem, but the benefits building up over several decades can be worth the wait.”

Becky Crew is an award winning science blogger and author of the forthcoming Zombie Tits, Astronaut Fish and Other Weird Animals (UNSW Press).
More information:
Landcare Australia

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