Bring Back the Beetles

Research Digs in to Improve Dung Beetle Survival

In a healthy ecosystem, dung beetles would not have to worry about where their next food source would come from.

Those who look around might think they see a healthy ecosystem. In reality, they do not because dung beetle populations are declining.

In Oklahoma alone, dung beetle numbers have decreased during the past few years. In 2014, when Wyatt Hoback, professor in the entomology and plant pathology department, arrived at Oklahoma State University, he began keeping records on the dung beetle population in the state.

“When dung beetles are around, they clean up the dung, which improves pasture health,” Hoback said. “They reduce parasites affecting cows like face flies and horn flies, and they also reduce internal parasite worms.”

Cattle typically will not feed within 5 or 10 feet of their own dung, said Greg Middleton, an entomology graduate student.

“Dung beetles are important in the nutrient recycling process that occurs when the dung gets decomposed back into the soil,” Middleton said. “The three different kinds of dung beetle all

perform the process in different ways, but all remove dung from the surface.”

The beetles that live in a fresh pile of dung are “dwellers.” Those that just dig holes at the edge of the pile and go straight underneath are “tunnelers.” Those that roll balls of dung away from the pile are “rollers.”

“To have a healthy dung beetle population, you want to have all the different sizes and all the behavioral groups,” Hoback said.

The dung beetle population is decreasing due to three primary factors: Ivermectin © , carbon dioxide levels and habitat loss, Middleton said.

“Ivermectin is the biggest issue for the beetles and is used as a pesticide for many cattle,” Middleton said. “Ivermectin is effective in controlling internal parasites, but it gets passed on easily in cattle dung. When dung beetles use the affected dung, it reduces their reproduction and the survivability from larvae to adults.”

A more recent study found higher levels of carbon dioxide reduced dung beetle size and survivability, Middleton said.

“Previous researchers looked at projections of carbon dioxide, what

he thought it was in the past, what it is now, and what he projected to be in the future, and he found a dramatic decrease in the adult size of the dung beetle and how many survived to adults,” Middleton said.

The third big issue facing the dung beetle is habitat loss.

“Fragmentation of forests and then urbanization reduces the amount of habitat for the sources of dung, so it’s not a direct impact on dung beetles but still is affecting the population,” Middleton said.

With the insects’ decline, Middleton set out to conduct research to conserve or save dung beetles, he said.

“One of the main goals was to determine a good way to collect dung beetles that would be cost-effective, such as pitfall traps,” Middleton said.

“The traps act as a trap door the beetles fall into,” Middleton said. “They are baited with dung because beetles are attracted to it.”

In Oklahoma, the ground is hard and mostly clay, making it more difficult to dig into the ground to install pitfall traps, Middleton said.

He designed three different traps, tested them, and proved which one would work best for this project.

“One of the ideas was to make the same one-quart container as a pit fall trap, place it on top of the surface, and then build plastic ramps on the side,” Middleton said. “The idea was when the beetles would smell the dung, they would walk up the ramp, they would fall into the cup, and that’s how we assess their population.”

This design had the most success compared to the other above-ground traps Middleton tried, he said.

The second part of Middleton’s research tested how prescribed burns influence dung beetle populations.

“From observational data, prescribed burns don’t seem to have a strong effect on dung beetles,” he said.

Immediately after a burn, the dung beetles preferred a nearby grass patch that wasn’t burned, Middleton said.

As the weeks progressed and the regrowth began, the dung beetles shifted back into those burned areas.

Part of the change may have been due to how quickly cattle and bison returned to those burned areas after new forage grew, he added. Those animals are the source of the dung so the beetles followed, he said.

“Dung beetles are useful, especially for farmers or just in general in

pastures,” Middleton said. “So, one of their main services — one of the more obvious ones — is to spread decomposed dung.”

In one night, a dung beetle can easily use 20 or more times its body weight, Middleton said.

A whole population of them in a pasture will quickly turn the dung back into the ground, allowing cattle to have many areas to eat, he added.

“Another service they provide is nutrient recycling,” Middleton said.

Nutrients, such as nitrogen and phosphorus, pass through cattle as they eat, Middleton said.

If those nutrients are not returned into the ground, the nutrients sit on the surface.

Dung beetles return the dung into the ground by their feeding, allowing those nutrients to once again be returned into the soil, Middleton added.

“We need to start thinking in more biological ways,” said Rodrigo Soares, an entomology graduate student.

Soares said he has worked with others in the department to research how dung beetles assist with biocontrol.

“Pest flies, like horn flies and face flies, use dung to reproduce, and they can also spread disease and cause a disturbance with the cattle,” Middleton said.

With dung beetles present, the amount of dung available for the flies is reduced, Middleton added.

“Many studies that have shown that in areas where dung beetles and flies were both present, the number of flies that emerged as adults was greatly reduced,” Middleton said. “One study even said up to 90%.”

In general, to help increase the dung beetle population, the best way to encourage population growth is to minimize insecticide use, Hoback said.

It does not matter the type of livestock operation you have, dung beetles can be found, Soares said.

Researchers at OSU are working to help preserve and eventually repopulate dung beetles, Middleton said.

“Mass-producing dung beetles is one goal for the research,” Hoback said. “We are looking for a really good way to breed dung beetles and supply the beetles back to farmers.”

Callie Keaton