Wheat midge predators find new home in Montana

U.S. researchers collect parasitoid wasps during Sask. field trip

A wheat midge outbreak in Montana recently sent two entomologists on a cross-border hunting trip into Saskatchewan.

Gadi Reddy and Brian Thompson of Montana State University were collecting parasitoid wasps in Saskatchewan wheat fields to take back and release in the state’s wheat producing areas.

“Around six years ago we started to get wheat midge inside the golden triangle wheat production area of Montana,” said Thompson.

“Previous to that, wheat midge had entered the Flathead Valley and caused major economic losses to that wheat.”

He said producers see natural predators as a good alternative to using chemicals.

“Our growers in the Montana Wheat and Barley Committee are very interested in projects like these natural biocontrol programs for reasons like reducing pesticide use, reducing environmental impact of pesticides,” he said.

A wheat midge looks like a small orange fly. It emerge from the pupae stage in late June and early July.

Female insects lay their microscopic eggs during the evening in newly emerged wheat heads when conditions are humid. The larvae feed on the developing wheat kernels when the eggs hatch.

Parasitoids are insects the size of flakes of pepper that kill their wheat midge hosts. They lay even smaller eggs inside the midge larvae and eggs and devour their hosts when they hatch.

Timing is key in controlling wheat midge, said Owen Olfert, a research scientist with Agriculture Canada in Saskatoon, because wheat heads are susceptible to wheat midge only between heading and flowering.

“If farmers control the wheat midge during that narrow window, they are able to conserve the parasitoid populations out there as well,” he said.

“On average, the main parasitoid controls 30 to 40 percent of the wheat midge population every year in Saskatchewan.”

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“That means a lot less insecticide is required during wheat midge outbreaks, and that implies less environmental impact as well.”

This is the second consecutive year that Reddy and Thompson have made field trips in Saskatchewan collecting the beneficial insects to take home and establish.

The first year they collected a population of macroglenes penetrans, the predominant parasitoid of wheat midge found in Saskatchewan.

This year they extracted a second complementary parasitoid insect, the Platygaster tuberosula species, which was successfully released in Saskatchewan at three locations 25 years ago.

“This year we came up to take what was released back in the 1990s and try to establish that parasitoid as well,” said Thompson.

“The idea is more parasitoids may cause synergism and control more of the midge population.”

The Montana researchers visited 25 fields in three regions of the province during their two-day trip, including Langenburg, where an abundance of parasitoids was found and collected. One particular field has not been sprayed with pesticides since the program began in the early 1990s.

The researchers dragged sweep nets across the wheat canopy for about 15 minutes per field, picking up parasitoids and all manner of insects.

“There’s a lot of insects in a wheat field: spiders, lygus bugs, flies like you wouldn’t believe,” said Thompson.

While Gadi drove to the next field, Thompson sat in the back seat with a cage and pooter (collection bottle), aspirating parasitoids from other insects.

Thompson said a major challenge was figuring out how to keep parasitoids alive between capture in one country and release in another.

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“Even the dry air the air conditioning creates is catastrophic to the insect samples,” he said.

“It took a lot of trial and error to keep them alive.”

Another difficult task was finding crops that were just starting to head so that wheat midges and parasitoids were present at the same time.

“We have the added problem that our crops are further along in Montana than they are here because of the latitude,” said Thompson.

“We had to find (Montana) farmers who had planted their crops late so they would be at the right stage to match up with the crops here.… They also had to have midge in their fields, which isn’t as big a problem as you think because the midge are pretty much everywhere down there now.”

Olfert said farmers are gradually reaping more benefits as parasitoids spread across Saskatchewan.

“There was a study in the 1990s that estimated farmers during those 10 years saved about $240 million by not having to spray (pesticides),” he said.

“If the wheat midge parasitoid diminishes the population below an economic level, farmers get a higher grade for their wheat.”

Added Thompson: “That’s not factoring in beneficial insects. Pesticides will kill just about anything… It’s hard to quantify how much that costs the farmers.”

Contact william.dekay@producer.com

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