On pasture ecosystems, the spotlight is often on grass and cattle, yet a well-functioning grassland may depend, at least in part, on behind-the-scenes work performed by dung beetles. With a skillset that includes converting manure into nutrients, improving soil aeration, minimizing pest flies and increasing water infiltration, dung beetles can help beef producers set the stage for efficiency.
Cattle manure is more than nutrients and water; it is teeming with insect life. “In the southern Prairies in Canada, you might find three hundred species of insects present in dung,” says Dr. Kevin Floate, a research scientist with Agriculture and Agri-Food Canada based out of the Lethbridge Research and Development Centre.
“Only some of those beetles are what we call dung beetles,” he explains, adding that dung beetles specifically feed on plant fibre in the dung. His lab is looking at how beef production practices affect dung beetle populations and their ability to do the dirty work that nature requires.
Most farmers are well aware that a beef cow can produce a lot of manure each day (up to 37 kilograms) depending on her size and diet. When manure isn’t quickly broken down, the nutrients are trapped and remain unavailable to plants for months or even years. Undegraded, intact manure also takes up physical space in a pasture, leaving forage in the immediate area less palatable.
Studies have also demonstrated that greenhouse gas emissions from manure, such as methane, ammonia and carbon dioxide, are higher in dung pats when there is no insect activity. It seems these tiny insects can play a big role.
There are three general categories of dung beetles. “Dwellers” spend their entire egg-to-adult life cycle in a cow pie and they can break down a manure pat in a few weeks or months. Both “tunnellers” and “rollers” arrive to a fresh pie as adult beetles, ready to tear apart manure pats.
As their name suggests, tunnellers dig tunnels beneath the pie where they bury dung. “They aerate soil and make soil more porous to water,” Floate explains. Rollers push the manure into small balls in which they lay their eggs.
Dung beetle populations vary by habitat and the animal’s diet. “On sandy soils, I expect to see certain types of dung beetles that I don’t expect to see on clay soils,” Floate says.
“When the cattle diet is made up of forage with more moisture in the early spring, that influences what species are present in dung. Later in the season, the forage has more fibre,” he says, explaining that species composition will shift again.
Tunnellers and rollers can efficiently break down a manure pat in a matter of days. This fast-moving conversion is key for reducing bothersome cattle parasite populations.
“Horn flies, face flies, and stable flies (to a lesser extent), lay eggs in fresh cow pies,” says Floate. “If dung beetles move manure quickly, this causes the cow pie to dry quickly and colonize with predation beetles that work to reduce pest populations of flies,” he says.
Destroying the manure also eliminates developmental habitat for these and other parasites, including internal round worms, which develop in manure pats and infect grazing cattle when the nematodes are consumed.
Unfortunately, some livestock insecticides that are commonly used to control beef cattle parasites have a negative effect on beneficial insects such as dung beetles. The impact of insecticide residues depends on the type of chemical used, such as moxidectin or ivermectin, whether the product is a topical solution or injectable, or if it has a sustained release mechanism.
“If you use a standard dose of pour-on ivermectin you will see reductions of general insect activity for 12 weeks and even up to 16 weeks after treatment,” Floate says. Not all insect species are affected to the same degree and some dung beetle populations may bounce back several weeks after product application.
Spring application of parasite control products causes the most problems for dung beetles. “For dung insects, they are most active in the spring when they come out from the end of May to early June, with a second peak of adult activity in August and late September,” Floate explains.
He notes that chemical residues from parasiticides in general change the chemical profile of manure, making it appeal to different dung insects.
“During collections, we might find the same insect species but they are present in a different relative abundance,” he says.
He and his team are currently working on a rigorous project assessing the trickle-down effects that a formulation of eprinomectin has on a cow’s rumen and subsequent manure. In this chemical, part of the active ingredient is formulated to pass quickly in manure similar to a typical ivermectin, but there is a secondary “pulse” of control that is also excreted one hundred days after application before tapering off. This detailed project is also looking at cattle treated with an antibiotic alone or in combination with eprinomectin and the impact these treatments have on the bacteria and fungi in the rumen and the resulting manure.
Dung beetle activity and development is highly dependent on weather, particularly during the overwintering phase of an insect’s life cycle.
“Earlier springs mean that dung insects ‘wake’ from their overwintering state earlier in the season and remain active later into the fall,” notes Floate. Warmer winters also mean a greater likelihood of insect survival through to spring. If winters get shorter or warmer, Floate predicts that additional species of dung beetles may be able to establish in regions of Canada and help to further accelerate the breakdown of manure.
In addition to his research, Floate is working on a dung beetle field guide for producers and ranchers. “When I first started learning about dung insects, I was looking for a guide or simple book I could pick up and get an idea of what’s in cattle dung and what the benefits are,” says Floate about the motivation behind the project. The field guide includes what species are present and where, identification tips and considerations about insecticide residues.
This summer, when producers are checking cattle out in the pasture, it might be worthwhile to stop and flip over a cow pie and observe these hard-working beetles.