Research Highlights

Research Highlights
Combatting the Dectes Stem Borer in Soybeans may Involve Key Plant–Insect Interaction

By Carol Brown

When a problem arises, one must look at the issue from several different angles to find the most effective solution. This is what entomology professor C. Michael Smith is doing to help farmers combat the Dectes stem borer. The soybean pest has been increasing its presence in Kansas fields over the last few decades and has become problematic in several Midwestern regions.

The Kansas State University distinguished professor emeritus is leading a multi-year research project, funded by Kansas Soybean Commission, to find solutions for better management of the soybean stem borer. The research team began by looking for soybean varieties that could be resistant to the pest, but over the years their path has taken a different direction.

“My colleagues have been working with the Kansas Soybean Commission for many years to find ways to reduce the impact that the soybean stem borer has in Kansas fields,” Smith says. “Larry Buschman and Randy Higgins, both entomology professors here at K-State, got me involved with this project.”

Their research journey has brought Smith to examine the soybean stem borer issue from another angle. After an unsuccessful search for resistant soybean plant varieties, he and colleague Lina Aguirre are looking at the pest itself and its genetics to alleviate the problem.

The Dectes stem borer larvae are found inside the soybean stem and feed on the stem tissue during the summer. Then in the fall, the larvae create a girdle, or line of tissue, at the base of the soybean stem, sealing themselves into a cavity for the winter. After a summer of eating plant tissue and weakening the soybean stem’s strength, the girdle weakens the stem even more. A good wind can then easily topple the plant, causing lodging problems at soybean harvest.

Entry hole in soybean stem from the Dectes stem borer. Photo: United Soybean Board

“Dr. Aguirre has found several unique genes in the digestive tract of the stem borer larvae that ‘turn on’ specifically to help them eat soybean stems,” Smith explains. He and Aguirre are partnering with Harold Trick, a K-State plant pathologist, to help with the project. Trick has been working on silencing these particular genes and may have achieved some success.

“Thanks to Dr. Trick’s efforts, we think we have some genes partially silenced. We have transgenic soybeans in the greenhouse ready for the borers to feed on and we’ll see if there’s any affect,” Smith says. “This is where our ‘leap of faith’ enters. We’re hopeful that when the larvae eat this tissue, it turns off their digestive genes, making them unable to eat soybean tissue.”

Many growers don’t know they have a soybean stem borer issue as plant lodging in the field can be indicative of several things. Farmers often don’t see the damage until it’s too late and it’s hard to document the loss when they don’t know why the plant has lodged, Smith says.

“Insecticides for the Dectes stem borer are not cost-effective because their application timing is critical,” Smith says. “The adult beetles are active on the plants for such a short period time. Once the larvae are inside the plants, aerial-applied insecticides can’t reach them.”

Two other team members, Drs. Brian McCornack and Jeff Whitworth, are exploring the improvement of insecticide effectiveness by adjusting application timing by learning more about egg-laying and flight behavior of the adult beetle.

Smith, his current team, and his predecessors have looked at the Dectes stem borer problem by searching known soybean germplasm and exotic varieties for pest resistance, looking at insecticide efficacy, and now also taking the avenue of turning off specific genes.

Because the Dectes stem borer is an increasing problem in the United States, farmers need to be aware if they have issues in their fields. This could help increase the demand for investments into the study of insecticide efficacy and host plant resistance. Smith encourages farmers to scout their fields for the soybean stem borer and report their findings, because it could help with awareness and, eventually, solutions.

Published: Sep 7, 2021

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.