Researchers to Relocate Parasitoid Wasps in Battle With Wheat Stem Sawfly

By Chabella Guzman

The Nebraska Extension held a Crop Production Clinic on Wednesday, Jan. 8, at the UNL Panhandle Research Extension and Education Center in Scottsbluff. The clinic featured presentations and research updates on crop issues and grower interests.

Among the topics for the day was ongoing research in battling the wheat stem sawfly. A native to Nebraska, the insect has become a big problem for wheat growers in the Panhandle. The High Plains Ag Lab (HPAL) has spent many years and extensive research on the sawfly done by Team Sawfly and Vinicius Zuppa, a graduate student. 

“One of the bigger findings we’re seeing under sawfly infestation is smaller wheat heads. So, not only are we losing yield to lodging and the inability to harvest. We're also seeing that it's actually taking a toll on photosynthate going up to the grain,” said Amanda Easterly, Nebraska Extension dryland cropping specialist.

A bright spot in the research is the increase in Bracon spp., a parasitoid wasp and natural predator of the sawfly, is beginning to make a dent in the infestation problem. In the Sidney area and southern Panhandle, the wasp has begun to show a measurable impact on protecting the grain yield. “The (wasp) is able to paralyze and incapacitate the sawfly larvae early enough to reduce damage,” Easterly said.  

Team Sawfly is investigating a new project that involves transporting the wasps in bales of straw to areas with sawfly infestations. The straw bales will come from the High Plains Ag Lab, which Team Sawfly considers a parasitoid wasp nursery. 

“We want to move those wasps, who will be in bales of straw. So that we can release those good guys into fields infested by sawfly,” said Pin-Chu Lai, Nebraska Extension Entomologist. “It's a big project that involves a lot of collaboration and expertise. So, we're excited and we'll be doing a lot of monitoring and moving straw around this coming season.” 

The European corn borer was another insect pest discussed at the Crop Production Clinic. This pest has not been a problem since 1996, when BT crops, including corn, were introduced, and the borer’s populations decreased. However, the insect is back on the Extension radar as it has developed some resistance to BT crops in Canada and the northeastern U.S. 

“The European corn borer is a small light-colored moth with small whitish larvae who have shiny black heads and some dark spots on them,” said Julie Peterson, Nebraska Extension Entomologist. “There are two generations a year, so for the first generation, you're going to be looking around June in your vegetative stage corn.” 

The borer caterpillar has a distinct feeding pattern that looks like small hole punches in a line across the corn leaves. As the caterpillar eats, it tunnels into the corn plant. The second generation appears at tasseling or just past tasseling, burrows into the corn stalk or the ear, and feeds, damaging the stalk or ear and decreasing yield.

Peterson said that while BT resistance by the European corn borer has not been detected in Nebraska, growers should be aware of it and be on the lookout for the pest.