Since 2007, the U.S. Department of Agriculture has been directing studies of a tiny Asian wasp called Trissolcus japonicus. These wasps are parasitoids of the brown marmorated stink bug (Halyomorpha halys), which has caused millions of dollars in damage to fruit orchards since it was discovered in the U.S. less than two decades ago.
Researchers have been conducting the wasp studies in quarantine laboratories to make sure they are not released into the wild until a full safety-assessment has been done. However, it looks like the researchers and their quarantine labs have been outdone by nature.
Trissolcus japonicus wasps were recently found in a public park in Vancouver, Washington by a field technician with Washington State University’s Tree Fruit Research and Extension Center, according to entomologist Elizabeth Beers.
“We did not expect to find this wasp here and are very excited about the discovery,” she said. “In the insect world, we struck it rich. Because the brown marmorated stink bug is not native to this country, it’s less likely that natural enemies exist here to destroy it. As it turns out, there’s one right under our noses.”
Josh Milnes, the WSU field technician, found the wasps on the leaves of a maple tree. They had just finished destroying the brown marmorated stink bug eggs that Milnes had left at a sentinel study site, said Beers.
Trissolcus japonicus wasps lay eggs inside clusters of stink bug eggs. After a wasp egg hatches, the larva eats the stink bug egg host, killing it in the process and then bursting out as an adult wasp.
Several T. japonicus wasp clusters have been found in Maryland and Virginia during the past two years, but it was surprising to find them in Washington.
“When I heard the news, I thought, ‘Oh my gosh, this is a biocontrol game-changer,'” said USDA entomologist Tracy Leskey in West Virginia, leader of the national stink bug research team. “The fact that the wasp showed up 3,000 miles away in Washington tells us that the stink bug’s natural enemy is deployed for attack.”
The discovery also suggests that the wasp was accidentally brought to this country multiple times, much like the very stink bug it destroys. Most likely, T. japonicus traveled in stink bug egg masses on plant cargo shipped from Asia, according to USDA research entomologist Kim Hoelmer, who studies the wasp species in a quarantine lab in Delaware. It’s also possible that an adult wasp or two hitched a ride on a jet and simply deboarded with the humans.
As scientists monitor T. japonicus to see how much it spreads in the field, research will continue in lab settings.
“We don’t want to introduce a non-native wasp that kills native stink bug species [that are] beneficial to our crops,” Hoelmer said.
In any case, the research looks promising so far, and T. japonicus seems to have potential as a biological control agent against the brown marmorated stink bug.