Dung Beetles for Cleaning Pasture

The rapid removal and processing of dung by introducing dung beetles can result in many benefits.

Sheep, cattle, horses, deer, goats and other domesticated livestock have been brought to New Zealand without the associated dung beetles that have evolved to process their dung. Intensive farming means large amounts of dung are continually being dropped onto the pasture surface. It has been estimated that pasture covered by cattle dung each day results in a daily loss of 570 – 950 hectares of grazing forage area. Depending on the time of year and climate, it may take dung pats weeks to months to break down and the adverse effects extend beyond the cowpat. A dung patch affects a grazing area five times its own area. Sheep and cattle reject pasture forage growing near animal dung, a response to the offensive properties of the dung itself. This is referred to as the zone of repugnance and it’s what some farmers try to offset by break feeding, a practice that increases livestock contact with diseases associated with dung.

Contamination of pastures by dung reduces the amount of forage available for grazing, and has other economic, environmental, ecological and social effects, such as pollution of waterways.

Various government agencies in the past focused on bringing in earthworms to help recycle dung from large animals, but they never gave a thought to dung beetles. Earthworms ended up being costly because earthworms don’t fly, so there was always going to be a problem getting them spread around the landscape.

Landcare research scientist Shaun Forgie got involved with dung beetles in the 1990’s. The basic idea was that dung beetles were far more efficient and faster at doing the job of recycling dung than anything else. They initially applied to bring in dung beetles in 1994 but that application was rejected and so the idea was shelved. Since that time there has been a lot more information available about the dung beetle’s impact on the pastoral ecosystem based on research done particularly in southern Australian pastures similar to those in New Zealand.

New Zealand does have a native dung beetle population. Various studies have shown that native dung beetles are often extremely abundant and play a key role in decomposition in New Zealand forests. They are not however, adapted to open pasture and occur predominately in native habitats, hence the need to introduce exotic species that are adapted to utilise the dung of grazing mammals in open pastures.

A number of countries that farm livestock on a large scale (particularly Australia, USA and Brazil) have benefited from importing pastoral dung burying beetles. Australia has a national dung beetle project that started in 1965, and has so far introduced over 50 species.

In February 2011, the Environmental Risk Management Authority (ERMA) gave permission for the importation of 11 species of dung beetle, with initial releases on properties in north Auckland, greater Wellington region and Southland.

At the time Federated Farmers was quoted as saying “The introduction of dung beetles would potentially enhance our production efficiency and sustainability by improving soil health and reducing the runoff into waterways,” The beetles also reduce greenhouse gas emissions from dung and urine.”

Organic carbon (dung) is buried and sequestered in the soil. Rapid manipulation and aeration of freshly deposited dung has the potential to reduce methane emissions from anaerobic bacteria in dung. Improved soil structure and biological activity from dung burial and tunneling by dung beetles enables greater infiltration and utilisation of nitrogen derivatives (e.g. nitrous oxide) etc. in urine.

John Pearce, owner of Shelly Beach Farm says dung beetles should have come to New Zealand 150 years ago with the first cows.   John is chairman of the group behind the project to release dung beetles.

A Mexican variety was introduced into New Zealand in the 60’s and became well established in Northland. Small numbers were subsequently released on Shelly Beach Farm in the Kaipara 15 years ago. That population of beetles is now abundant and spreading to neighbouring farms in the area.

Dung beetles have enormous potential for positively assisting New Zealand’s greenhouse status. They can contribute hugely to the mitigation of issues regarding cattle effluent and runoff, thereby adding some validity to the country’s “clean green” image when it comes to livestock agriculture.

Subsequent importation of dung beetles and their release has been established by the Dung Beetle Release Strategy Group, which was established in New Zealand by a group of farmers and other interested parties in 2008, with the objective of importing and releasing dung beetles to assist with the removal of pastoral dung of agricultural livestock. A project to import and breed up these beneficial insects was funded largely by MPI’s Sustainable Farming Fund. Landcare Research has provided science and technical support to this programme.

Now with the programme at an end, a newly founded company called Dung Beetle Innovations has been created by members of the DBRSG including John, to continue the process of mass rearing on a commercial scale. They will also research the importation of additional species, oversee releases and encourage farmer consultation. Post release monitoring and research will be in conjunction with landowners, Landcare Research, GO’s (eg. Beef and Lamb NZ) and NGO’s.

Beetle tunneling leads to increased aeration of the soil allowing water and surface inputs such as urine, fertilisers or dung, to penetrate better. Tunneling and dung burial also result in increased grass root growth and biological activity in soils under and adjacent to dung pats. Dung beetle activity therefore leads to reduced surface run-off and better retention of dung and urine in the soil. This in turn results in reduced microbial contamination in run-off, less leachate and non-leachate pollution and reduced eutrophication of waterways, ponds and lakes.

Landcare Research has also done some field trials on the effect of dung beetles on the parasitic nematode life cycle in various soil types. Shaun says there’s compelling evidence from this research and many studies abroad to suggest that dung beetle activity can significantly reduce the survivorship and re-infection rates of nematodes. The primary cause for these reductions are likely via a combination of mechanical damage through dung manipulation by adult beetles; desiccation of eggs and larvae in dung during manipulation of dung at pasture surface by adults; feeding by dung beetle adults and larvae or, through removal of dung containing eggs and larvae to areas where the probability of nematode emergence is reduced (e.g., deep burial beneath the pasture surface).

The introduced species Onthophagus binodis is active from late spring to autumn. Fattened mature grubs will overwinter in the dung balls in which they have developed underground. If the soil temperature is not too cold, these will continue to develop slowly into new adults which will emerge when spring arrives. Some adults will also overwinter in underground burrows. On mild days some adults will come to the surface to feed and top up their fat reserves for winter.  They prefer fresh firm to liquid cattle dung, and are also attracted to fresh sheep, horse, goat and alpaca dung.

The adults build nesting galleries in tunnels approximately 20 cm below the dung pat. Each tunnel is packed with several brood balls each with one egg.

Development from egg to adult takes 8-10 weeks depending on the soil temperature. There are at least two generations a year.

Shaun says there are some simple pre-requisites needed before you seed your farm with a starter colony of dung beetles. The idea is that farmers purchasing colonies will receive a colony or colonies of male and female beetles onto their property. The farmer needs to offer his new guests a sheltered, centrally located, northern facing portion of the farm with a ready supply of fresh dung . This is a dung island and will encourage the dung beetles to stay rather than fly off to the next nearest fresh dung supply.

Following the introduction Shaun says farmers need to make sure stock is nearby or rotated to adjacent pastures so that the dung beetles can follow a fresh supply of dung. At least some stock should be within the vicinity of the release location around the time the new generation of beetles is due to emerge.

Information regarding this is available by visiting the dung beetle website, dungbeetle.org.nz; and farmers receiving beetles will be consulted by staff at DBI.

Dung beetles co-exist with other bugs and beetles. They are not affected by grasses or endophytes and are simply using the soil as a medium to breed in. The larvae of the dung beetle don’t attack pasture like the black beetle. Shaun says the larvae of tunneling dung beetles are encapsulated in a ball of dung so they don’t feed on pasture roots.

A number of studies show a significant increase in earthworm populations, weight and biomass and the depth at which they occur, following dung beetle introduction.

To establish dung beetles on farms, some simple modifications of existing drench programmes may be required. Active constituents in drenches can persist in dung for several weeks and can have varying degrees of toxicity to dung beetles, depending on the method of application. For example dips, pour-ons and injectables result in the highest doses absorbed into animals and are thought to deliver the greatest volume of residual chemicals in dung. The drench type is also important. Moxidectin (a macrocyclic lactone) and most anthelmintics are generally not harmful to dung beetles. however, some synthetic pyrethroids can cause high mortality in adult beetles for up to a week or more after treatment and therefore have potential to significantly affect beetle populations.   The key is to be mindful of the type of drench, its frequency of use and target only the shedders when establishing dung beetles.

Farms that have just established a breeding colony of dung beetles in the centre of their farm may benefit from isolating the treatment group(s) to a ‘quarantine’ or outlying downwind paddock well away from the initial release area or growing population area, where dung beetles may be less likely to find them during the critical period following treatment with a high-risk chemical.

Other farming practices that reduce pasture contamination by the infective stages of livestock gut parasites, such as cross or rotational grazing, should also be considered to help reduce reliance on drenching. Over time the need for drenching should decrease, as parasitic reinfection of stock will decline if thriving dung beetle populations are present.