Large increase of brown marmorated stink bugs poses serious threat to Oregon crops

The amount of invasive brown marmorated stink bugs in 2022 tops anything that was seen in Oregon for at least five years and poses a serious threat to Oregon crops and garden plants, according to Oregon State University Extension Service's orchard crop specialist.

Nik Wiman, an associate professor in the College of Agricultural Sciences, said fruit and vegetable crops in the Willamette Valley have been affected.

"It's unusual for brown marmolated stink bugs to feed on fruit and vegetable crops," he said. "There have been a lot of damaging populations of BMSB in hazelnut orchards. Growers use preventative measures so we're surprised we've seen so many."

It's unclear why the population exploded this year, Wiman said. Like other insects, the population of the shield-shaped brown marmorated stink bug (BMSB) varies from year to year depending on climatic factors. The extremely wet spring most likely contributed to it, but the increase could also be attributed to a natural cycle.

Native to Asia, BMSB was introduced on the U.S. East Coast in the late 1990s – probably by ship – and has spread to almost every state in the country, including Oregon in 2004. The insect feeds on at least 170 plants, particularly vegetables, pears, apples, and hazelnuts, but also ornamentals. Its name describes the odor they emit when they're crushed.

Oregon's hazelnut industry, valued at $132 million in 2020, is one of the state's crops hardest hit by the invasive bug, according to the Oregon Department of Agriculture. The state's problem echoes the situation in Turkey – the world's leader in hazelnut production – as well as Italy and the country of Georgia, said Wiman, who researches alternative practices for controlling BMSB, including biological control, habitat manipulation, trap crops, and barriers.

One promising biological approach is the samurai wasp (Trissolcus japonicus), an insect native to areas of Asia where it keeps the indigenous BMSB population under control. Scientists have discovered the wasp in the United States and Oregon, where it was initially distributed across the state by Wiman and a team of scientists at OSU and elsewhere. The Oregon Department of Agriculture is now leading the effort.

The parasitic wasp hunts for the egg masses of the stink bug and lays an egg inside each egg in the mass. The wasp develops inside the egg, effectively killing the stink bug, and then chews its way out. OSU Extension has a short publication on the wasp and its effect on the stink bug.

In addition to agricultural crops, the stink bug shows up in homes in autumn when they are looking for a warm, dry place for winter.

"We've done an analysis of reports we get from people," Wiman said. "We've looked at the timing and by far and away we get the most BMSB reports in the fall. Adults are at their peak and are trying to get into houses. Warm fall weather gives more opportunity to get into buildings. They can be very annoying when they are coming into homes, and they may fly around inside your house all winter. Then they come out in spring."

Wiman advises homeowners to seal all cracks where the stink bug can enter and vacuum up inside infestations. On outdoor buildings, washing them off with a strong shot of water will keep some at bay. If they come back, spray them again.

Farmers and homeowners can serve a key role in samurai wasp research by collecting possible brown marmorated stink bug egg masses and reporting them.

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Kym Pokorny, Communications Specialist for Oregon State University

Public Service Communications Specialist