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Wasps provide simple fly-control
option for dairy goat owners

By Tim King

With the end of spring and beginning of summer comes the unwanted nuisance of flies in some parts of the country. Swarms of flies can frazzle the patience of dairy owners and their goats during peak fly breeding season. Stacy Erickson, who has a herd of 35 Saanens, Alpines, and Oberhaslis near Salinas, California, found a simple, non-chemical, solution to the problem. She buys parasitic wasps and has accomplished a dramatic reduction in fly numbers on her farm with them.

"It gets cool in the evenings during the summer here," Erickson said. "The flies settle on the wall of the barn. I went out to count them one evening and I could only find twenty. Before I got the wasps, they used to just cover the walls and doorway into the barn."

Erickson’s previous attempts at fly control were largely unsuccessful.

"Last year I had four to six fly traps hanging over the main area where the goats are and the traps would fill at least once a month," she said. "In the evening the string that the traps hang from was thick with flies. The traps did reduce the adult population somewhat but they really didn’t get at the source of the problem."

Parasitic wasps do get at the source of the problem. They seek out the thousand of fly pupae lying in decomposing manure, bedding, or feed. When they find them they lay one or more eggs in the pupae. The wasp eggs hatch and become larvae before the fly larva have time to emerge as adults. The wasp larvae eat the fly pupae. What comes out of the rice grain sized fly pupal case is one, or more, adult wasps. The wasps, which are about the size of an ant according to Erickson, then seek out more fly pupae to lay eggs and start the process over.

There are a number of species of tiny, naturally occurring, parasitic wasps that prey on the pupal stage of flies breeding around manure and other decaying organic matter such as feed and bedding. In nature, unfortunately, there are never enough of the non-biting, and non-stinging, wasps to reduce barnyard flies to a level that is comfortable for humans and their livestock. To solve that problem goat owners can import more wasps.

"The wasps are nocturnal and it’s likely you’ll hardly even know they are there," said Mic Grandfield, a partner in The Source, a 25-year-old business supplying beneficial insects to agriculture.

The Source sells what they call colonies of wasps. Erickson uses one and a half colonies from The Source every four weeks from February through October to keep flies in, and around, her barn under control. Each colony contains about 80,000 wasps. All three species of wasps that The Source uses in it colonies are naturally occurring throughout the 48 contiguous states of the U.S. but different life cycles of the two insects makes it unlikely naturally occurring wasps will ever control fly swarms around average barns and loafing lots.

"The flies have a distinct advantage in actual numbers produced," Grandfield said. "A single fly will lay up to 900 eggs but a single parasite will attack less than fifty fly pupae. Additionally, the life cycle of a fly is much shorter than that of the parasitic wasp. This contributes to the pest’s advantage in reproductive capability."

Grandfield also explained that the wasps are not strong fliers and don’t travel far from where they emerge from the fly pupae.

"Because of all this it’s necessary to offset the flies’ natural advantages by maintaining a high level of parasites in the fly breeding site," he said.

Terry Davenport, a representative from Tucson, Arizona based beneficial insect supplier ARBICO, agreed.

"A female fly can lay up to 1,000 eggs but a wasp only lays between 20 to 40 eggs," she said.

ARBICO, like The Source, ships fly larvae that have been parasitized by wasps across the US and overseas. They call their shipments units but the amount of parasites in an ARBICO unit and a colony from The Source are approximately equal.

"The insects are shipped as parasitized pupae in a sawdust medium and are dispersed by releasing a small handful at hot spots such as manure collection sites, under water troughs, along fence lines, below straw bedding, around mill areas, silage pits, and other feeding sites," Davenport said. "At the edges of these hot spots scratch a half inch hole in the ground with your boot heel, drop in a small handful of sawdust and pupae, and cover them with straw, earth, or manure to protect them against wind, birds, or pesticides."

Erickson places her colonies from The Source, which come mixed with wood shavings, around the edges of the manure pack in the goat’s loafing lot and near the barn door.

"I try not to leave it in the direct sun," she said. "Even though there is a little bit of goat traffic there it doesn’t seem to matter."

Mic Grandfield, from The Source, said that rain won’t hurt the colonies but putting them in puddles of water may.

Both companies recommend replenishing the parasites every two to four weeks depending upon fly concentrations. Erickson has obtained good results with new wasps every four weeks. But the primary reason for her success, she believes, is that she started before the weather brought on any significant fly population. In Salinas fly season peaks in May when the weather is both warm and moist.

"I got one and a half colonies at the beginning of February-we hardly ever even get frost around here-and have been doing it once a month since then. This is the best result I’ve ever had but I never started that early. I didn’t start until June last year and the flies were going pretty good by then."

Erickson said people at The Source will guide livestock owners through the amount of wasps they need for the number of animals they have.

"The staff has been extremely helpful," she said. "My total cost this year will be $250 but I think it’s worth it."

The wasps have some limitations. Grandfield tells customers that the wasps will not control flies, such as deer flies and horse flies that spend their life as a pupa in the water. They will attack pupa of houseflies, biting stable flies, garbage flies, little houseflies, blowflies, face flies, false stable flies and horn flies. The wasps are also susceptible to fly insecticides. Both companies recommend discontinuing spraying around fly breeding areas if livestock owners use wasps.

Although the tiny parasitic wasps have brought the flies under control at the Erickson farm, The Source, and ARBICO, still recommend traps for the few adults that may hatch on Stacy’s farm or fly in from her neighbors. In fact, if livestock owners have neighbors with a serious fly problem there’s not much that can be done to control the flies that travel from the neighbors. Both companies also recommend maintaining good sanitation and manure management as part of an over all fly control strategy.

For more information on parasitic wasps to control flies contact:

The Source BioLOGICAL Fly Control, 19025 Black Oak Lane, PO Box 491703, Redding, CA 96049-1703. Ph: 530-243-8547, 800-380-3560; fax 530-241-7848; info@sourcebiofly.com; www.sourcebiofly.com.

ARBICO; http://store.arbico-organics.com; 800-827-2847.

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