Parasitic wasps urged as way to control flies

Horticulturist works with chicken and hog barns and cattle farms as well as feed mills to control flies in spilled grain

As soon as the weather warms up, the flies arrive, making yards and barns miserable spots for people and livestock.

Saskatoon horticulturist Patricia Hanbidge has been using parasitic wasps to help control fly populations on farms and acreages for about 30 years.

When her children were young she was looking for control methods other than insecticides that could kill more than the targeted insects and possibly make the farmyard unsafe for the kids.

“Biological controls aren’t for everyone that’s for sure, because it’s not an instant fix,” she said. “It’s something that you do over time that kind of forms a balance that’s reasonable. It’s not that you don’t have any flies but you have very few of most of the species of flies.”

She has had clients with chicken barns, hog barns, cattle farms and more. Feed mills use parasitic wasps to deal with flies in spilled and rotting grain.

“They really do work,” Hanbidge said.

There are native parasitic wasps but not in enough numbers to control flies.

Imported parasitic wasps target species like house and stable flies that don’t breed on animals, but breed in manure, rotting vegetation, pen bedding and other places where they subsequently irritate livestock and can limit animal growth.

They don’t sting. They are tiny, about the size of a pinhead, Hanbidge said, and most people who use them don’t even see them.

“Most of the biological controls are very specific, so in this case the parasitic wasps only go after the pupa that the fly is incubating in,” she said.

The wasps lay eggs in the fly pupa, the eggs hatch and eat the fly larvae and then the wasps complete their life cycle.

This breaks up the life cycle of the flies to reduce the numbers.

Releasing them at this time of year is best in order to get ahead of the flies, but control can begin at any time.

For example, a hobby farm owner came to Hanbidge for help a couple of years ago in mid-summer. They released a large number of wasps, along with some adult fly traps, and within two weeks there was a noticeable drop in flies.

The next year, they released fewer wasps and this year, fewer again.

“I have experimented stopping using them and seeing how long it takes and within one season you’re back to where you were before you started,” Hanbidge said. “Maintaining some degree of biological control seems worthwhile.”

While most insectaries recommend releasing wasps bi-weekly, she makes different recommendations based on her years of experience, the extent of the problem and the environment.

She buys her wasps from insectaries that breed a specific mix for the prairie environment.

“If you use it properly and kind of get a good balance, you can reduce the number of parasitic wasps that you put out and still maintain that control,” she said.

More people are turning to biological controls as they hear of pesticide-resistance or want to use more environmentally friendly methods.

“If nothing else, this whole COVID pandemic has taught us that we maybe need to take better care and make better decisions,” said Hanbidge. “Using alternative methods that give you long-term control or balance in the situation are always better than a quick fix.”

Hanbidge is known for her time with the University of Saskatchewan horticulture program. She is now the lead horticulturist at the non-profit Orchid Horticulture.

She has always favoured biological control in her horticultural work. She prefers to bring in bugs bred at reputable insectaries rather than those gathered in the wild. She said if not done properly, wildcrafting can upset the natural population.

During the COVID-19 pandemic, Hanbidge has begun a Facebook live presentation each Wednesday at 1 p.m. CST on the Orchid Horticulture page to help people with gardens and other topics. She also has started a YouTube channel called Grow.

To contact Hanbidge about parasitic wasps or Orchid Horticulture, email or call 306-931-4769.

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