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Wasps to the rescue

Japanese wasps released in Medford to battle orchard pests
Andy Atkinson / Mail Tribune Entomologist Max Ragozzino talks about wasps being introduced in an attempt to control brown marmorated stink bugs, which have invaded Southern Oregon.
Andy Atkinson / Mail Tribune Entomologist Max Ragozzino dumps tiny Japanese wasps Wednesday on maple trees lining the LDS orchard near Delta Waters and Foothills Road in Medford. The wasps are a natural predator of the brown marmorated stink bug, an invasive species that threatens local crops.

A tiny Japanese wasp was released Wednesday in a north Medford pear orchard with hopes that it will help combat a big problem — spread of the brown marmorated stink bug, which is a threat to many agricultural crops and a nuisance for homeowners.

The Samurai wasp, Trissolcus japonicus, measures just five-hundredths of an inch long. The wasp is a parasite that injects its eggs into stink bug eggs. When the baby wasps hatch, they eat the stink bug eggs. The wasps are not harmful to humans.

Max Ragozzino, a biological control entomologist with the Oregon Department of Agriculture, brought 165 of the wasps from Corvallis, and he was joined by Rick Hilton, entomologist with the Oregon State University Extension Service in Jackson County. They sprinkled the wasps on maple tree branches at the edge of the orchard site.

Wednesday’s release was the first by the state Agriculture Department in Oregon, but the Extension Service has done releases over the years both locally and in the Willamette Valley.

“We want to release enough wasps at each site so it’s worthwhile, not a sporadic approach,” said Hilton. Releases were done locally in 2017 at a number of locations in the valley, but they got established at just one location in Talent, followup research showed.

Ragozzino said he would have been happy to release 1,000 wasps, but they must be raised in a laboratory. He plans to return to the Rogue Valley at a later date to release more wasps. One site might be in Ashland’s Lithia Park, but that would require approval from the city’s Parks and Recreation Commission.

Brown marmorated stink bugs are native to Asia. They first appeared in North America in 1996 and in Oregon in 2004. They caused major devastation to East Coast agriculture in 2010.

Pears that have been attacked will take on a so-called “dog faced” appearance and have a hard texture, while the inside will be mushy.

“You name it, they will eat it,” Ragozzino said of the long list of plants the stink bug will consume, including pears, other fruits and many vegetables. They can damage young trees by boring into the bark. Home gardeners have reported damage to beans, cucumbers, raspberries, hops and some ornamental plants.

The stink bugs tend to seek warm places in the winter, and will often be found inside houses. When weather warms, the bugs look for nearby vegetation.

“They’ll do very well with this neighborhood,” said Hilton, noting the proximity of houses to the orchard. “Everywhere I have looked for it, I have found it at some level. It loves residential areas that have lots of trees.”

The Samurai wasp attacks the stink bugs by injecting eggs inside bug egg clusters in tree canopies, leaving larvae that chew their way out as they develop.

Wasps were transported to Medford in takeout soup cups. A dab of organic honey was placed inside the cups to attract the wasps, which are pollinators that eat nectar. Mesh screens on top of the cups were made from chiffon fabric, as commercially available material is not fine enough to prevent escape.

“A lot of food storage things tend to be safe for insects,” said Ragozzino.

In Asia the stink bug is not a big problem because the wasp keeps it under control. But in the United States it is a different story. Other states are also doing wasp releases.

After the 2010 outbreak, studies were started to see if wasp introduction would cause problems. But then wasps were discovered to have established themselves naturally in a few locations, possibly hitching over with the stink bug.

“For once we got something accidentally introduced that is very helpful,” said Ragozzino.

U.S. agricultural organizations are hoping that the efforts here will have a similar effect to what has occurred in Asia, where the Samurai attacks are estimated to be 60% to 90% effective in parasitizing egg masses.

Any major reduction in current stink bug numbers would likely take at least five to 10 years, said Ragozzino. The two organizations will be tracking how the populations fare. They use bright yellow cards with a sticky substance that attract the wasps, so scientists can verify their presence.

Reach Ashland freelance writer Tony Boom at tboomwriter@gmail.com.