At a secret location just north of Auckland, an experiment has started which might alter the face of New Zealand's $12 billion dairy industry.
In a collection of blue plastic containers, imported insects are chewing their way through piles of cow manure on a Rodney farm.
Netting over the bins is designed to stop the insects - species of dung beetles new to New Zealand - escaping into the wild.
Passionate advocates of the field trial - they include farmers, scientists and those who will profit from selling the insects - claim the beetles eventually could save the country millions each year, cut greenhouse gases, reduce the runoff of chemical-rich nutrients from dairy farms into streams, curtail the use of drenches and lift soil fertility.
Andrew Barber, project manager of the Dung Beetle Release Strategy Group, believes the insects "will bring about one of the biggest changes in New Zealand farming this century."
But according to scientists who harbour grave doubts about the work, the insects could expose children and the elderly to potentially severe disease such as E coli and salmonella, put dogs at risk of a nasty bug, and deliver little in the way of economic benefit.
If anything, say these scientists, the dung beetle project is a risky experiment which should never have got to the point where pieces of shadecloth stand in the way of the insects' liberation.
The beetle project has echoes with previous plant and animal releases in New Zealand. Opossums from Australia have laid waste to large areas of native forests and spread Tb, deer have eroded South Island high country, German wasps displaced native colonies and gorse has become a costly nuisance.
So what lies in store from the dung beetle project?
For two years, ever since a Government agency gave the green light to the release without controls of 11 species of imported dung beetles, debate about the wisdom of the decision has been confined to researchers, policy makers and backers of the heavily taxpayer-funded project.
All that changed last month when persistent critic and Auckland University science dean Professor Grant Guilford went public with his misgivings. He slammed the import decision as "deeply flawed" and a "spectacularly reckless departure from the overriding precautionary principle that should take precedence in the face of uncertainty".
Reaction to his call to put the whole scheme on hold while doubts were resolved has sparked spirited debate on chatroom threads.
After he remarked that his "veterinary bones" told him insufficient duty of care surrounded the issue, one backer of the project wrote: "I am utterly gobsmacked that the Dean of Science's critique of what has been a careful, scientific and refreshingly open process comes down to his 'veterinary bones'."
Guilford, who spent two decades with the vet school at Massey, taps into a network of high-powered scientists. Until last year, he sat on the board of Landcare Research, a Crown research institute whose own enthusiastic staff helped assemble the case for importing, breeding and releasing the beetles.
Guilford quit Landcare, he says, so he could step outside the somewhat entwined approval process where one agency, using public funds, supported a private applicant to New Zealand's biosecurity gatekeeper, the Environmental Risk Management Authority (Erma), now the Environmental Protection Authority.
The three-member authority panel was advised by the dung beetle applicants that the insects would pose no public health risk. This assertion was made simply by ticking a box marked "no" to the question: "Can the organism cause disease, be parasitic, or become a vector for human, animal or plant disease?"
Last year, Auckland's medical officer of health, Dr Denise Barnfather, having belatedly been advised of Erma's decision, wrote to Landcare pleading with the agency to proceed with caution.
She was concerned the introduced winged insects - unlike flightless indigenous dung beetles - could spread notifiable diseases to rural water tanks and directly among inquisitive children tempted to munch on a dead bug. Eight thousand homes in the Auckland region use tank water, and thousands more beyond its boundaries.
Barnfather, a public health medicine specialist, urged Landcare's chief executive Richard Gordon and chairwoman Jo Brosnahan: "Until the significance of these potential human exposures to pathogens harboured by dung beetles are adequately researched and understood, public health recommends that a precautionary approach is taken and that exotic dung beetles are not introduced into New Zealand." Approached for comment, Landcare said the appropriate agency was the EPA.
The Auckland public health chief is rather on her own. At the Ministry of Health in Wellington, Dr Darren Hunt, acting director of public health, said the ministry was aware of her concerns, and believes the appropriate forum to address these is through the EPA.
EPA principal scientist Geoff Ridley said: "The Ministry of Health was notified of the application and call for submissions, but did not make a submission.
Rigorous science supports the expert panel's decision to allow the release of the exotic beetles.
"It is not unusual for different experts to come to different conclusions about decisions on the release of new plants and animals. However the application went through a robust process, and the EPA stands by the decision."
He also noted that "Grant Guilford chose not to make a submission on the application to release the dung beetle species.
He subsequently contacted us to voice his concerns about the decision, but when we assessed the information he provided it did not materially change the original risk assessment, and so there was no reason to take further action".
Fifteen years ago, an attempt was made to import dung beetles by a scientist who argued the insects would speed up the removal of manure from paddocks.
At the time, however, the Ministry of Agriculture's regulatory arm - the predecessor of the EPA - knocked back the application because not enough research had been done to satisfy biosecurity experts that the insects would deliver all the benefits claimed for them.
Guilford maintains nothing has changed in this regard. The difference this time, he argues, was the role of Landcare scientists advocating for the scheme then providing "independent" advice to ERMA.
He maintains the approval process accepted anecdote, failed to investigate risks and did not do peer-reviewed research. He thinks a "hot potato syndrome" kept other scientists off the case as controversy could affect career prospects.
On the issue of submitting to the approval process, Guilford remarked that "like most others I just assumed they would be doing a good job on behalf of us all. I only heard of the DB proposal many months after the Erma approval and didn't begin to look into it until a sufficiently wide group of people began approaching me".
Guilford is not alone in his concerns. Papers show Fonterra and Dairy NZ, the industry's lobby group, have reservations.
At Auckland Council, biosecurity manager Jack Craw says he does not know the location of the trial beetle plots. He would expect to, he says, because the exotic beetles could make their way into pockets of bush where native dung beetles live.
He was surprised no conditions were imposed to monitor the beetles.
"We haven't been kept fully informed of the trials," said Craw.
"It's odds on they will be harmless. But the point is we don't know and that's not good enough. You don't gamble with these things."
Asked about these complaints, dung beetle manager Barber, who chairs a technical advisory group overseeing the Rodney field trials, says Craw was part of the group which approved the trial design. Its members got a progress update in January, and a letter from Landcare's Richard Gordon in February with an update on wider developments, including public health issues.
Barber said: "As chairman of the TAG I have not received any correspondence from Mr Craw about his concerns."
Away from the undisclosed trial plots, the group is rearing vast numbers of the beetles ready for release, some in winter, and in greater numbers next spring and summer. Barber will not reveal the location of the fieldwork because, he says, debate about the project "has brought out some extremely odd people. The farmer definitely does not want his location disclosed."
Documents circulated by the strategy group put the cost of beetles at $1 to $2, and suggest that farmers will be up for $5,000 to $10,000 to establish colonies on their land.
Guilford says the country faces an experiment which might - or might not - work, and risks to human and animal health which remain unresolved.
"The cavalier approach damages the future trust in biocontrol."
Diet of droppings
Dung beetles, as their name suggests, live and breed in animal droppings. Generally, they prefer certain types of dung. Advocates of the New Zealand project say the 11 species they can release target cow dung, through critics say at least one species breeds in dog and human dung.
New Zealand has a dozen or so flightless native species which mostly live in forests. Three introduced species exist, which the Environmental Protection Authority (EPA) says have a similar ecology to the new species. The EPA says there are no documented cases of these existing species posing a risk to human health, or to the environment.
Again however, not everyone is convinced the exotic insects will be utterly safe, or as the EPA determined, carry "negligible" risks.
Adult beetles chew through dung and bury it down tiny tunnels below the cow pats. Eggs are laid in dung balls carried into the tunnels, from which new adults emerge. This cycle, say backers of the beetle project, will hasten the breakdown of dung, free up more pasture for grazing, reduce runoff and flooding by making it easier for water to infiltrate the ground and make farming cleaner and healthier by reducing the infective stages of livestock diseases on farmland.
The EPA was told by submitters opposed to the release the claims were just that - claims. NZ had wetter soils than Australia - where the beetles were collected - used drenches which could kill the insects and had worms which did the job. One submission called the cited benefits "exaggerations beyond belief".