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Can dung beetles rein in cattle’s methane emissions?


Dung beetles were introduced from Europe to save us from being buried in manure. Now researchers believe they might also help us mitigate greenhouse gas emissions. Belinda Smith reports.


Cattle produce 300 million cow pats a day.
IPG GUTENBERGUK LTD / GETTY IMAGES

When European settlers brought cattle and sheep to Australia, they didn’t just bring food sources – they brought veritable poop factories. The solution to the problem came in the form of foreign dung beetles. The University of New England’s Min Raj Pokhrel aims to find out how the little critters are faring – what temperatures they prefer and how they might mitigate greenhouse gas emissions – in the New South Wales Northern Tablelands.

A single cow poops about 10 times a day; with about 30 million cattle in Australia, that’s 300 million cow pats plopping daily onto the ground. In Europe, cow dung is polished off by dung beetles. Adult beetles bury it, eat it and lay eggs in it, so their larvae can also feed on it once hatched. Digging dung into the ground also has the benefits of dispersing grass seeds, not to mention fertilising and aerating the soil, letting water more easily soak into the earth and giving plant roots room to grow.

Even though the nation boasts more than 400 species of dung beetle, none were up to the task of dealing with cow poo. Native dung beetles evolved with marsupials such as wallabies and kangaroos. Adapted to hard, small, fibrous poops, they couldn’t deal the big wet splats from cows.

DUNG PATS WITHOUT BEETLES PRODUCED METHANE EMISSIONS FIVE TIMES HIGHER THAN THOSE WITH.

Without introduced dung beetles, splattered dung would foul paddocks, shrinking grazing land and providing perfect breeding spots for disease-spreading flies and parasites. Pats, once they harden on the ground, can sit there for months – even years.

Hungarian entomologist George Bornemissza noticed this in the 1950s when he first set foot in Western Australia. Less than 200 years after cattle had been introduced to Australia, cow poop was a problem of epic proportions. Bush fly populations were becoming unbearable, and farmers were forced to contend with rising worm and bacterial infections in cattle stock.

In Europe, poop just wasn’t such a big deal. Bornemissza wondered if Australia could enlist some outside help. Would introduced dung beetles clean up after cattle?

He had to tread carefully. Introduced species have a habit of running out of control in Australia. After a decade of researching dung beetles from around the world, the first large-scale release took place in 1967. Four species – a total of 275,000 beetles – were let loose, mostly in northern Australia between Broome in Western Australia and Townsville in Queensland.

Since that first cluster almost 60 different dung beetle species have been introduced from Africa, Europe and Asia, the most recent being Onthophagus vacca, in 2014, and Bubas bubalus, in 2015.

Dung beetle (Scarabaeus sacer) hard at work.
GALLO IMAGES-ANTHONY BANNISTER / GETTY IMAGES

So how are the introduced beetles faring – and what about their native counterparts? These are questions Pokhrel aims to answer during his PhD research.

He is taking stock of their populations, counting them in 10 locations across elevations from 300 metres to 1,300 metres above sea level in the Northern Tablelands. Even at the highest altitudes, Pokhrel exclaims, “We still found them!”

He is also monitoring when are they most active – do they prefer the summer heat or the chill of winter? – and how far introduced beetles, which are quite good flyers, have spread.

He’s also getting his hands dirty. Part of his project is determining what type of poop native dung beetles like. Has their appetite changed with the availability of sheep and cow dung? So far, he’s found some native dung beetles have developed a taste for sheep poop. This may be because sheep dung is more nutritious compared to that from kangaroos, he says, or perhaps the native dung beetles have adapted to wetter, less fibrous poops. There’s still more work to do before drawing a conclusion.

Pokhrel is also keen to uncover what it is about different species’ poop that attracts dung beetles. He thought water content might play a role, so to test this he mixed sheep and kangaroo droppings with water to make them the same consistency as cow pats.

“They looked the same for me, but it was very different for dung beetles,” Pokhrel says. Dung beetles that preferred sheep droppings continued to favour them, even in their sludgy state. Likewise, cattle-specific beetles stuck to their usual, even with watery sheep and kangaroo poop on the menu. So how do greenhouse gases fit into the equation? Cows burp and fart methane – a greenhouse gas 28 times more potent than carbon dioxide – but their dung can pump it out too.

Grasslands and pastures are usually carbon sinks, with plants taking up carbon dioxide for photosynthesis. But cover even a fraction of a paddock with cow pats and it becomes an emitter. On top of this, methane-producing microbes prefer an oxygen-free environment – precisely what a sloppy, dense cow pat provides. If the pat is broken apart and aerated, perhaps by a dung beetle looking for a place to lay its eggs, then carbon dioxide-producing bacteria take over.

European and US studies have shown this to be the case. Six-day-old dung pats without dung beetles produced methane emissions five times higher than those with the beetles. Pokhrel will see if this applies in the Australian context – and might find yet another reason to celebrate nature’s recyclers.


Belinda smith 2016 2.jpg?ixlib=rails 2.1
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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