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Bug Off:


Parasitic wasps are gaining recognition as an environmentally safe means of fly control.

By Kevin Heiser

Ninety-eight percent natural control of the housefly already exists according to a 1964 article by University of California, Riverside, Professor Fred Legner. Without natural control, the world would be 47-feet-deep with flies in five months.

Imagine having an employee who can continuously kill flies for more than two weeks at a time, who doesn't need a pesticide applicator's license, who is always on time for work and who never gets in anyone's way.

Now imagine a barn or a feedlot full of these workers, tiny gnat-sized wasps, able to kill immature flies in manure before they emerge as bothersome adult flies.

Fly parasites are being used in all sizes of livestock operations from one-horse barns to 100,000-head feedlots. In some cases, the wasps are used in place of insecticides; in others, they are part of an integrated management system using wasps to control breeding flies and poison bait to control migrating flies.

History of Beneficial Bugs

Beneficial insects have been used in field crops for the past century to control everything from alfalfa weevils to sugarcane borers, but it wasn't until the last decade that fly control has become popular.

In the 1950s it became clear to the U.S. Department of Agriculture that there were long term effects of extended use of pesticides, the Agricultural Research Service says.

Failures of insecticides such as DDT, which cheaply controlled more than 500 pests, but left residue in meat and milk, caused the USDA to shift its research to focus more on biocontrol, a way to use natural enemies of insects to reduce their populations.

The ARS estimates that since 1953 biocontrol has saved more than $2 billion in pesticides.

Hitch Feedyard manager Chip Newell of Guymon, Okla., says he used only chemical control until three years ago. "But we quit that for several reasons," he says.

"It requires a certified applicator, it's very easy to spray something wrong, it ties up one or two people at least one day each week and it's not very effective because after three days it wears off," Newell says.

Newell uses biocontrol because it works, but he also feels like it's environmentally safe.

"It seems like the ecological thing to do. It's very much in harmony with nature. We're not putting pesticides or anything in the air," he says.

How Biocontrol Works

A parasitic wasp's single ambition is to reproduce. And since wasps are dependent on fly pupae for reproduction, it is essential that a balance be maintained between wasp and fly populations.

When a wasp finds a fly pupa, it uses its stinger, also called an ovipositor, to break a hole in the puparium. The pupa dies once it is exposed to air.

The wasp takes a meal from the pupa and lays an egg inside which eventually hatches and feeds on the immature fly. The wasp eats only twice during its 16 days to 28 days as an adult.

The mature wasp is ready to carry on the reproductive cycle as soon as it emerges from the puparium, but since the fly's life cycle is much shorter than the wasp's, it is necessary to release additional wasps periodically in order to balance the populations.

An adult fly can lay as many as 2,400 eggs during its lifetime and these eggs hatch within seven days to 10 days.

The average parasite lays from six eggs to 350 eggs per day which can take as long as two weeks to three weeks to mature.

Wasps are available from several commercial insectaries nationwide. Clients receive paper bags filled with wasps in the pupal stage packed in wood shavings. The shipments are normally weekly, but there is no exact method for control, says entomologist Frank Junfin of Kunafin insectary in Quemado, Texas

"There's not a formula," Junfin says. "It's not like a label on a pesticide bottle."

Kunafin specializes in custom designed integrated insect control, Junfin says. "We've grown our own insects since 1959," he says.

Junfin visits his clients on a regular basis to make sure the system is working.

"Our clients can't control the weather conditions that influence fly populations, but they want results. We have to be able to adjust and ship more parasites if necessary," Junfin says.

Wasps are distributed in the favorite breeding areas of flies-moist, compact manure and decaying vegetation.

Adele, Junfin's wife and Kunafin consultant, says the parasitic wasps are not what most people think of when wasps are mentioned.

"The stinger is not like a bee's; it's actually like a drill bit and its only purpose is to penetrate the hard shell of the fly pupa. The stinger has nothing to do with penetrating people's skin," she says.

It Really Works

"It's not a cure-all, but it's cut our fly population by 75 percent," Newell says.

Hitch Feedyard has used an integrated system of parasitic wasps and fly bait for three years.

"There are always flies," Newell says, referring to flies that migrate from the surrounding area. "But the number is down substantially and we don't have the cattle irritation or the people irritation that we used to have.

"Everybody used to habitually carry a fly swatter in our office building. You always had one or two flies in your office and now we seldom have to worry about it," Newell says.

"It's probably 1 112 times the cost of chemical, but we don't have to figure in any labor, time or effort on our part," he says.

Veribest Cattle Feeders Inc., Veribest, Texas, Chief Executive Officer Wes Bonner says migrating flies were a problem when he began using biocontrol nine years ago.

"It took a couple of years to get good control," Bonner says. "We had lots of migrating flies from our neighbors, but baiting helped control them.

"It's very evident that there are fewer flies around now that we use the wasps," he says.

Bonner says there is no comparison between biocontrol and chemical control.

"The chemical system might have been more expensive, Bonner says.’ We spent a lot of money seasonally on chemicals; we'd wear out a big sprayer every couple of years, plus we had to pay for the labor."

Horse barn manager for Fiesta Texas theme park in San Antonio, Texas, Craig Flanders says an integrated program of pyrethrin spray and 15,000 parasitic wasps from Kunafin each week is working well in the newly constructed barn.

"I haven't seen a fly in here for two months," Flanders says.

One of the park's many restaurants is less than 100 yards away from the barn, necessitating top-notch fly control, Fiesta Texas pest control foreman John Machen says.

"We can't tolerate flies in the food service areas; the guests won't stand for it and neither will I," Machen says.

Improved Animal Performance

A USDA study shows that calves gain less when they have to contend with flies.

Test calves gained 0.2 pound per day less when pestered by approximately 50 stable flies. When the number of flies was doubled, gain was reduced by 0.48 pound per day.

The incidence of fly-transmitted ailments such as pinkeye can be reduced by stepping up control measures, USDA says.

New Mexico dairyman Jeny Settle says that his cows were bugged less when he switched from chemical control to biocontrol.

"The year we sprayed, I know I lost 2 to 3 pounds of milk per cow per day," he says.

Adele Junfin says its results that matter to cattlemen. "No matter how convenient or environmentally safe we make fly control, the degree of control will always be the determining factor," she says. "Without good results and economic incentive, we can't persuade anyone to reduce their use of chemicals."

 

 

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