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Unique beetle can invade soybean stems

John Obermeyer, Purdue University Extension entomology Dectes stem borer
INSECT CURIOSITY: Entomologists describe the Dectes stem borer as an interesting, attractive insect. It’s been detected inside some soybean plants but doesn’t cause economic damage.
Entomologists assure the Dectes stem borer is more of a curiosity than an economic threat.

Some entomologists refer to the Dectes stem borer as a unique, attractive insect. Steve Gauck, Beck’s sales agronomist, Greensburg, Ind., considers it more of a novelty that he finds from time to time, typically in southwest Indiana. He found a few stems affected by the beetle in that region again in 2017.

When it invades a plant, the stem borer can hollow it out and disrupt nutrient flow. However, it doesn’t normally attack widespread areas, either within a field or across a large geographic area.

“We know it is out there, and it may be a concern if you find it in your field,” says John Obermeyer, Purdue University Extension entomologist. “However, I have never seen a situation where it has caused economic damage.”

While most reports of the beetle come from a few southern Indiana counties, the insect isn’t confined to that geography, Obermeyer says. “We have found it in Tippecanoe County in the past, but it wasn’t causing economic damage.”

Most people can classify the Dectes stem borer as an insect that shouldn’t cause panic in terms of threatening widespread crop damage, Obermeyer says. It will affect some plants where it occurs, but damage won’t rise to levels that would justify spraying for the beetle. In other words, its presence or the damage it causes doesn’t reach an economic threshold high enough to justify the cost of insecticide and an application.

Gauck sometimes carries a stem hollowed out by the beetle in the back of his truck. He uses it as an example of an insect that may show up in a localized area, but that you don’t normally have to worry about in terms of taking any action.  

HOLLOW STEM: Steve Gauck of Beck’s found this soybean stem hollowed out by the Dectes beetle while scouting in southwest Indiana.
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