Take care of your dung beetles and they’ll take care of your cows

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Farm Forum

New South Dakota research suggests the chemicals some producers use to control parasites such as intestinal worms in livestock and to suppress flies have a negative side effect – they suppress beneficial insects that do the same work for free.

That’s one implication of a master’s degree study at South Dakota State University by Jacob Pecenka, who is carrying out the study under the direction of Jonathan Lundgren, a research entomologist at the U.S. Department of Agriculture’s North Central Agricultural Research Laboratory north of Brookings.

Lundgren said the research focuses on insects such as dung beetles that remove livestock manure, or dung, making soil nutrients available sooner and denying a breeding place for flies, for example.

“We’ll be studying the economics of dung removal. We’re going to see how quickly these dung insect communities can recycle the dung pats. A lot of these farmers are seeing that sometimes their dung pats will last for years. That means they’re a resource for pathogens. Those dung pats are a resource for flies and they foul the pastures. So we need to recycle them as quickly as possible,” Lungren told the Capital Journal.

“On some of the more progressive ranches I’ve experienced, their dung pats are recycled within four to seven days – that’s before any parasites or flies can complete their development. So we could, in theory, be able to eliminate a lot of our pesticide inputs into cows if we were to be able to harness these things.”

Scientists already know such insects make a difference in the bottom line. Researchers John E. Losey and Mace Vaughan, in a 2006 study published in the journal BioScience, calculated that dung beetles save U.S. ranchers about $380 million annually through the work they do moving dung underground.

But no one in the region has studied the issue of late. Pecenka said the last study by a South Dakota State University researcher on anything similar was in 1976.

Pecenka said his study looks at 10 farms in eastern South Dakota that use different management styles for their pastures.

Though the dung beetle may be the poster child for the study, Pecenka said his work looks at the entire community of insects and other arthropods – spiders included – that make use of the dung or feed on other insects such as fly maggots that depend on dung.

Management makes a clear difference in the abundance and diversity of insects in dung, which in turn makes a difference in how quickly insects can break down the dung pat or move it underground.

For example, in pastures where producers are known to use anti-parasite drugs called ivermectins, Pecenka said he might find a few dung beetles in a single core – a sample of dung and the earth underneath, taken with a golf cup cutter – compared to perhaps 30 or 40 dung beetles in a similar sample taken from a pasture where cattle are not treated with ivermectins. He won’t have the exact numbers to compare management systems until he has counted and identified the insects in his samples, but the differences are already apparent, he said.

Many producers use products to control the intestinal parasites and to suppress fly populations.

“But if you have a healthy population of dung beetles, the dung beetles themselves will do a lot of those things. They break apart that pat and get it into the soil or they consume it,” he said.

That eliminates a site for flies to lay their eggs. Dung beetles, beneficial predators called rove beetles and spiders also feed on fly larvae. Tiny parasitoid wasps lay their eggs in fly pupae so that the young fly never hatches at all.

If those beneficial insects are thriving in a grassland, Pecenka said, there is less chance that the larvae of intestinal worms, hatched from eggs that have passed through the animal in the manure, can migrate to nearby grass stems to be ingested by other cows.

In addition, Pecenka said, the study will shed light on techniques such as rotational grazing and “mob grazing” – running a group of animals into a small pasture area to essentially mow it clean – compared to other management systems. One benefit of mob grazing is that the large concentration of animals in a given area attracts a lot of insects to process that waste that the animals leave afterward; but before parasites can be a problem, the animals have moved on.

Quite often producers who don’t use ivermectins are rotating their cows to reduce the risk they will get parasites, Pecenka noted.

“It’s a really tricky network. The people who are taking a risk and figuring it out, I think they benefit from it because they don’t have those input costs,” Pecenka said. “The insects are doing the job for free. You don’t have to pay those guys, you just have to give them a good place to live. They’re really beneficial.”