A natural predator of the invasive brown marmorated stink bug has found its way into Oregon on its own, discovered recently by the Oregon Department of Agriculture. Meanwhile, a four-year effort to rear the tiny wasp at a quarantine facility at Oregon State University for future controlled releases continues with the hopes that the natural spread of the biological control agent will speed up the process of gaining permission from the US Department of Agriculture to deploy the wasp. Any introduction of the good bug– Trissolcus japonicus– is welcome news to Oregon, whether intentionally released by ODA or naturally spread among the growing population of the exotic stink bug. “We’ve been rearing these wasps in quarantine since 2011 and no releases have been made anywhere in the US yet,” says ODA entomologist Chris Hedstrom, who is the one who discovered the natural presence of T. japonicus this summer. “We still need permission from USDA’s Animal Plant Health Inspection Service. Right now, we are putting together a petition for release because we have enough data to make a first attempt at gaining permission. Growers are worried about the stink bug. Some have already been impacted and they are looking for a biocontrol solution.” It has been a race against time ever since brown marmorated stink bug was first discovered in 2004 as a home pest in Portland. Additional sightings were soon reported in other urban areas. In recent years, populations of the exotic stink bug have exploded and spread to other parts of Oregon. Homeowners often report hundreds of the pests in or around their house. Additionally, brown marmorated stink bug has become a significant agricultural pest for the first time in Oregon. “Last year, we started to get a first response from growers who were seeing what they thought was stink bug damage,” says Hedstrom. “Specifically, a lot more stink bugs were showing up in hazelnut orchards and we’re finding the same situation this year. We haven’t seen huge amounts of agricultural damage like there is in the mid-Atlantic states, but we are bracing for the worst.” Brown marmorated stink bug, left unchecked, has already blazed a trail of destruction in states like Pennsylvania, where major losses have been reported for apples, peaches, grapes, tomatoes, and many other fruits and vegetables that also grow in Oregon. The list of crops and plants the stink bug won’t feed on is probably shorter than the list of crops and plants it likes. The pest even feeds on maple and cedar trees. The biological solution everyone is hoping for has been pursued in the laboratory nationally with ODA as one of three lead regional agencies conducting research involving T. japonicus, the imported wasp that acts as a parasitoid of the brown marmorated stink bug. The tiny wasps were collected from Asia– also home to the exotic stink bug– and provided by USDA’s Agricultural Research Service (ARS). The research program established a colony of the good bugs as well as a colony of brown marmorated stink bugs. It was confirmed that the adult female tiny wasp lays its eggs inside the stink bug eggs. As a result of the parasitization, the stink bug eggs do not survive. While the biocontrol agent holds great promise in the control of brown marmorated stink bug, there has been concern that the tiny wasps might have a similarly negative impact on native stink bug species. Not all stink bugs in Oregon are bad, and researchers want to make sure non-target species are not affected. With the pending petition to USDA, ODA will be making the case that only the right stink bug species will be impacted. In 2014, T. japonicus was found in the mid-Atlantic states for the first time outside of a quarantine facility. There was suspicion that a breach had occurred, but it was proven to be a different population of the beneficial insect that had been introduced unintentionally. Last year, Washington State University researchers recovered the wasp in Vancouver. Again, there was worry of a quarantine breach, but DNA analysis showed it was a different population of the wasp from the one being reared by researchers and even different from the one discovered on the East Coast. A second unintentional introduction of the tiny wasp had apparently taken place. “We got excited but had not found it in Oregon until early this summer when it was recovered from traps near downtown Portland,” says Hedstrom, who was the first to find the wasp inside the state. In looking for the wasp this year, ODA placed sentinel egg clusters throughout the state. Hedstrom found one parasitized stink bug egg cluster that was completely obliterated. “We don’t usually see that in the field because there are not a lot of native natural enemies that could have killed the stink bug. We put more traps out in the area. Within a couple of days, wasps were attacking those egg clusters. We brought the wasps back to the lab and had them identified as T. japonicus.” It appears the natural spread of the wasps has not gone very far, but the insect’s presence is encouraging. If researchers can find out more about the population of T. japonicus, it could accelerate the timetable for getting permission for small-scale releases of the reared biocontrol agents. “We’ve been working on this biocontrol agent for so long and trying to get it released, it’s really exciting to now find it already here and attacking exotic stink bugs in the field,” says Hedstrom. Even with the wasp naturally coming into Oregon, ODA would like to complement its spread through targeted releases of the insects being reared in quarantine right now. That combination would certainly speed up the ability to control the pest. “In 10 years, assuming biocontrol releases are allowed, we should see a population decrease of brown marmorated stink bug,” says Hedstrom. “There could be smaller pesticide applications or less impact on crop yields to the point where growers could absorb any damage. Homeowners might no longer see them in the thousands, but only perhaps a handful in the house and something that can be easily managed.” That may be a best case scenario, but it’s one that researchers are starting to be confident of.
