Wes Bonner sits in his office at Nolan County Feeders in Roscoe, TX, north of Sweetwater, and watches a housefly go idly about its business. For a brief moment, he thinks back to his childhood, when a housefly buzzing about produced a screen door opened in invitation and a flurry of great entertainment as the youngster took a fly swatter to arms.

Bonner still has a fly swatter close at hand and is by no means opposed to a little entertainment. But as a feedyard manager with nearly 40 years' experience, he's sadly aware that a fly swatter ranks pretty low on the list of effective control measures when fly season comes around.

That's why, since 1980, he's used biological control as the foundation of his fly-control efforts. While he no longer manages a large finishing yard but instead owns and manages a backgrounding facility, he still uses parasitic wasps to control both his fly problem and costs.

Nolan County Feeders began life as a 21,000-head finishing feedyard. When Bonner took over some years back, he realized its size plus its location in Central Texas, with no packing plant nearby, put him at a competitive disadvantage to the larger feedyards in the Texas Panhandle.

But drawing on his experience running a larger feedyard, he knew that biological control of flies using parasitic wasps works. Even with the seasonal nature of the backgrounding business and a tight labor market that effectively limits the number of calves he can adequately care for, he's found biocontrol of pest flies is still feasible.

“The way we're running this yard, the conditions aren't that much different from a finishing yard,” he says. That means the conditions for flies aren't that much different, either.

Generally, those conditions are decaying material for the flies to lay their eggs, and enough moisture to keep things suitable for the pupae to complete their cycle and grow into adult flies. “If the manure's dry, you're not going to have any larvae,” he says. But even in Bonner's arid climate, if you put enough cattle in a pen, you've created fly nirvana.

How it works

The two main flies of Bonner's concern are the housefly and the stable fly. The housefly reproduces in manure; the stable fly uses decomposing vegetation, such as waste hay from a round bale feeder, to lay its eggs. Entomologists say fly parasites will control both species.

The tiny parasitic wasps and other beneficial insects used in biological fly control lay their eggs in the fly pupae. The parasitic larva consumes the fly pest's larva, and an adult parasite emerges and repeats the cycle. Since the parasites attack only the pupae, adult flies won't be affected. The life cycle of a housefly, for example, is around 21 days, which means it takes a while for biological control to begin working.

That can be a problem, especially with stable flies that migrate many miles. “If there are other facilities that will breed flies within several miles, you're going to get those flies,” Bonner says. “So you may be doing a good job and still have flies.”

While Bonner isn't spraying, since widespread use of pesticides will kill the parasitic wasps as well as the pest flies, he uses fly bait along the roads, in the shaded areas outside the pens and in the feedmill. The parasites aren't attracted to the bait, so it doesn't affect them. And entomologists say limited use of pesticide spray, especially to get residual control on walls where stable flies tend to go after taking a blood meal, is acceptable.

Bonner initially began with biocontrol of flies because it was cost-effective. At his old yard, he took advantage of a turnkey service with the company that supplied the parasitic wasps, which freed up his employees to do other things. At Nolan County, with fewer cattle in the pens, they can distribute the parasitic wasps themselves. “Here, because we're much smaller, they ship us wasps weekly and then we're applying those in the yard where we think it will be the most beneficial.”

In the fly wars, the weekly shipments are akin to reinforcements brought from the rear to the front lines. Once the existing fly population is reduced, the number of parasitic wasps will also decline because they no longer have hosts. As new flies migrate to the feedyard, it's necessary to keep sufficient parasites on hand to deal with new incursions.

Even with using his own labor to distribute the parasitic wasps, spread the fly bait and do the other chores associated with his fly-control program, Bonner estimates his costs are at least 25% less than alternative measures.

According to Bonner, biocontrol for flies works in pasture situations, as well. He's been on stocker operations that had cattle turned out on pasture, at stocking rates of around two head/acre. “They were using wasps to control their fly problem and felt like it was working,” he says.

Entomologists say that when you're dealing with flies, keeping them controlled at levels below an economic threshold is the goal. You'll never eradicate them, no matter how hard you try.

But Bonner isn't dissuaded. After all, he still has a fly swatter.