Dung beetle mania
Excrement-loving dung beetles, rolling their balls of animal poo across the ground, could one day become a familiar sight on New Zealand farms. These unlikely critters may help solve some of the environmental problems created by agriculture as well as improving farm productivity.
Scientists at Landcare Research have been studying the beetles for some time and have recently received money from the Ministry of Agriculture and Forestry’s Sustainable Farming Fund to import and release dung beetles into New Zealand.
How dung beetles use poo
Dung beetles use the faeces (poo) of animals for food and reproduction. Not all dung beetles make their burrows in the ground and then roll the dung home for burial. Most species will actually dive into a pile of dung and then make tunnels in the soil beneath the faeces, dragging as much dung as they can into the tunnel with them. The dung beetles use the buried poo to lay eggs in. Some adult females will break the dung into smaller balls (called brood pears) and lay an egg in each pear before covering it in a mixture of dung and saliva that hardens like cement to protect the egg inside.
As the eggs hatch, the grubs feed on the dung. They break it down and eventually turn it into a sawdust-like material that adds to the fertility of the soil structure while getting rid of dung sitting on top of the ground.
Too much dung is a problem on farms
Shaun Forgie and Hugh Gourlay (researchers from Landcare Research) say that, while dung decomposes naturally, intensive farming means large amounts of dung are dropped. This can lead to environmental problems such as leaching of nutrients into waterways and reduced pasture production because of increased forage fouling. Livestock such as sheep and cows will not graze around their excrement, and this, in turn, reduces pasture productivity.
Dung beetles help with the poo problem on farms
“If we successfully introduce and establish exotic dung beetles in New Zealand, we expect that, in the long term, there will be millions chewing and burying dung from pastoral animals such as cows and sheep and that means a monumental management change for our farmers,” says Mr Gourlay.
“I suggest it would, in fact, be one of the biggest changes to our farm management since we first imported cows into the country. This is a bold statement but the impacts of an army of efficient dung-burying beetles could be profound.”
That is because dung beetles have many potential environmental and economic benefits including improved soil health and reduced run-off. Increased aeration and water penetration into the soil, through beetle tunnels, reduces urine and liquid dung run-off, reducing microbial contamination, leachate pollution and eutrophication of waterways. An army of dung beetles would also reduce nitrous oxide emissions. Livestock poo accounts for 20% of New Zealand’s N2O emissions, and 80% of the nitrogen content of dung is lost as vapour when dung sits on the pasture surface, compared to only 10% following burial by dung beetles.
As mentioned, dung beetles also improve pasture productivity, and the burial of manure also enhances grass growth, reducing reliance on fertiliser inputs. Solid fertiliser is one of the biggest working expenses on most conventional livestock farms. In addition, studies have shown that dung beetles reduce fly pests and human disease. Nuisance flies breed in dung but are out-competed for resources by fast dung-burying beetles. In Hawaii, introduced dung beetles reduced dung-breeding pest flies by as much as 95%.
There will also be reduced infection of livestock by parasitic worms that are normally spread through faeces. The beetle chewing and burying of dung kills almost all of the parasites that infect our farmed animals. This would reduce the need for and expense of drenching livestock.
Services provided by dung beetles that remove cattle dung were worth an estimated US$380 million per year to the US economy (USA has almost 100 million cattle – New Zealand has 10 million). In Australia, they have imported some 45 species of dung beetles from around the world to successfully deal with their cattle dung problem.
No native dung-burying beetles in New Zealand
New Zealand lacks native pastoral dung-burying beetles. A tropical species Copris insertus was introduced in 1956 but only established at Whangarei, probably due to poor climate-matching. Two accidentally introduced Australian Onthophagus species are widespread, but have little impact, presumably because they are poorly adapted to feed on pastoral dung. They are small beetles that bury less dung and don’t build up high enough population densities.
There are thousands of different species of dung beetle, and they are found all over the world (except Antarctica). Different species have preferences for different types of dung because of the environments in which they live. Pastoral dung beetles feed on poo that is found on all pastoral farms. The scientists from Landcare Research are looking at this group to work out which species would be happy in our range of cooler climates.
The dung beetle project
The first step of the 3-year project is to choose between 5–12 species that will work effectively in a variety of climates throughout New Zealand and then apply to ERMA (Environmental Risk Management Authority of New Zealand) to import the beetle. If successful, researchers will then import, mass rear and ultimately release beetles into the field in the 3rd year.
“This will initially be in the Rodney and Southland districts because that is where our farmer-based community group and our co-funders are, and then we’ll be focusing on releases through all parts of the country,” says Mr Gourlay.
Between 1969–84, CSIRO Entomology introduced exotic dung beetle species to clear pastures of accumulated livestock dung on Australian farms.