The Asian micro-hymenopteran wasp, Trissolcus japonicus, is considered the primary parasitoid of the brown marmorated stink bug (BMSB) Halyomorpha halys, in its native region of origin. Asian fruit growers consider BMSB as only a secondary pest of apple, likely due to the suppression of native biological controls that include Trissolcus japonicus.
After the severe tree fruit losses from BMSB in the mid-Atlantic in 2011, a survey of parasitoids was conducted in Korea by a team of USDA researchers including lead entomologist Kim Hoelmer, who collected this species of wasp and has been studying this species under quarantine in the USDA laboratory’s in Newark, Delaware. Trissolcus japonicus has been under quarantine and has shown limited negative impact on our native predatory stink bug complex, and is considered a viable biological control candidate for release to control BMSB in the U.S.
In a 2014 survey of resident egg parasitoids of the BMSB by Don Weber (ARS-Beltsville Area Research Center) using sentinel stink bug egg masses revealed that T. japonicus was present in the wild at one of his study sites in Beltsville, MD. Since then, several T. japonicus wasp clusters have been found in Maryland and Virginia over the past two years.
More recently, it appears that T. japonicus was found in Vancouver, Washington, by a field technician with Washington State University’s Tree Fruit Research and Extension Center, according to entomologist Dr. Elizabeth Beers. Josh Milnes had placed BMSB egg masses on the leaves of a maple tree in Vancouver, first on Aug. 14 and again on Sept. 23. that had become infested by T. japonicus.
In the article in WSU News, Dr. Beers stated that the discovery implies the wasp was also imported to this country, possibly on multiple occasions, much like the very stink bug it preys upon.
Kim Hoelmer offers the plausible explanation that T. japonicus traveled here undetected in stink bug egg masses on plant cargo shipped from Asia. It’s also possible that an adult wasp or two hitched a ride on a jet and simply deboarded with the humans. Regarding the impact that this wasp may impose on our native predatory stink bug complex Hoelmer states, “We don’t want to introduce a non-native wasp that kills native stink bug species beneficial to our crops,” he explained. So far, however, the research (on T. japonicus) looks promising.
Entomologists across the mid-Atlantic will likely continue to monitor T. japonicus to see how much it spreads in the field and what impact on other beneficial insects this invasive may have. The HVRL also will begin a monitoring effort in 2016 in the lower and mid-Hudson Valley to determine if the decline in BMSB we are seeing in both urban and agricultural environs can, at least in part, be attributed to this newly invasive (and warmly welcomed) parasite.