CORVALLIS, Ore. — The samurai wasp may be small, but it is a mighty assassin of one of Oregon agriculture's most detested pests — the brown marmorated stinkbug.
No bigger than a pinhead, the tiny wasp lays its eggs inside the eggs of stinkbugs, killing the host when they hatch. Stinkbugs first arrived in Oregon in 2004 and are a scourge to farmers, damaging high-value crops including wine grapes, blueberries, cherries and hazelnuts.
Researchers know the samurai wasp can be an effective biological control for stinkbugs. A new study from Oregon State University goes a step farther, describing how farmers can integrate the wasp as part of an overall management strategy.
David Lowenstein, an entomologist and postdoctoral research associate at OSU, led the study, which focuses on the impacts of different insecticides on wasp survival. His results found that some chemicals were highly lethal to the wasp, while others were more suitable.
The study was published recently in the Journal of Economic Entomology. Funding came from the Oregon Hazelnut Commission, Oregon Raspberry and Blackberry Commission and the USDA Specialty Crop Research Initiative, which is assisting more than 50 researchers across the U.S. studying ways to defeat the stinkbug.
Like the stinkbug, the samurai wasp is native to east Asia. It was discovered in 2016 in the Willamette Valley, and since then OSU has bred colonies of the wasp in Corvallis and at the North Willamette Research and Extension Center in Aurora, Ore., to distribute to commercial orchards.
"They are not available commercially," Lowenstein said. "We're the sole group that is rearing the parasitoid and trying to get it established in different parts of the state."
However, Lowenstein said it does no good to distribute the wasps while farmers are spraying certain types of insecticides to control other pests.
For the study, Lowenstein tested the effects of nine insecticides on samurai wasps in lab and field trials. He said neonicotinoids and pyrethroids were "fairly toxic" to the wasps, while diamide insecticides were less toxic.
One reason for this is because diamide insecticides specifically target sucking and chewing insects such as filbertworm larvae in hazelnut trees, while neonicotinoids and pyrethroids are "broad-spectrum" insecticides, Lowenstein said.
"The application of this work is that, for someone who wants to benefit from biological control from the samurai wasp, first they're going to have to time it around when they apply insecticides," he said. "We don't expect chemical insecticide use is going to go away. It's just how can you integrate them together."
Lowenstein also suggested that orchards maintain natural areas around the property where samurai wasps can retreat during crop spraying.
Stinkbugs are found in 24 of Oregon's 36 counties. OSU has already distributed samurai wasps at 63 locations across the state for bio-control.
The wasps are not harmful to humans and do not sting people, Lowenstein said.
"There's no way you are going to confuse this with a yellowjacket," he said. "If you have a samurai wasp on your property you won't even know it's there unless you are seeing its effect, which is less stinkbugs."