Wheat farmers have a new weapon against a pest that costs them $350 million a year; researchers are using straw bales to move tiny parasitoids into fields and fight the wheat stem sawfly

For wheat farmers in parts of the Great Plains, one of their most damaging pests may have met an unlikely enemy: another insect. The wheat stem sawfly, Cephus cinctus, is a major pest of wheat, with the US Department of Agriculture’s Agricultural Research Service (ARS) estimating that it costs wheat growers about $350 million every year. With limited means of control, the pest has expanded its range and caused major damage to dryland winter wheat crops in Colorado and Nebraska.

Now, Agricultural Research Service (ARS) researchers and their university colleagues have tested a simple way to move the sawfly’s natural enemies into areas where farmers need them most. In a 2025 study published in Arthropod Management Tests, researchers evaluated whether baled wheat straw could be used to transport and release Bracon parasitoids, insects that naturally attack wheat stem sawflies, into infested wheat-growing areas.

The idea: Move the pest's natural enemy

The approach turns something farmers already have, wheat straw, into a delivery system for biological pest control. Researchers first identified areas where Bracon populations were established. They then harvested wheat straw, baled it and transported the bales to locations in Nebraska and Colorado where wheat stem sawflies were present.

The idea is that Bracon parasitoids emerge from the straw and begin searching for wheat stem sawflies. Rather than relying entirely on conventional pest-control methods, farmers could potentially use the insects' natural behavior against the pest.

The ARS team worked with the USDA’s Animal and Plant Health Inspection Service to move the straw. At the ARS field station, nine straw bales produced roughly 67,500 parasitoids.

The research paper concluded that swathing, baling, transporting and spreading wheat straw can be a viable means of introducing Bracon into new habitats for the biological control of wheat stem sawfly in wheat production.

Why the parasitoids matter to wheat farmers

The wheat stem sawfly causes problems by attacking wheat plants, while Bracon species are natural enemies of the pest.

That makes the technique potentially useful in places where sawfly populations are already causing serious losses and farmers have limited control options.

Once released, the parasitoids can attack wheat stem sawflies in the surrounding fields. In the researchers' experiment, they found evidence that the Bracon released from the straw reached wheat beyond the immediate release area.

At the Colorado field station, wheat stems sampled 35 meters into the field showed 5.9% parasitism. At the Nebraska farm, samples taken 50 meters into the field showed 26.6% parasitism. The researchers also observed higher parasitism at field edges than farther inside the fields.

That matters because the goal is not simply to release insects, it is to establish a population capable of attacking the pest in the wheat landscape.

For wheat farmers facing a pest that costs the industry hundreds of millions of dollars each year, that could turn an ordinary byproduct of the harvest into a surprisingly useful tool. As the ARS puts it, the goal is to “increase wheat yields in heavily infested areas of the Great Plains.”