Joshua M. Milnes, Nik G. Wiman, Elijah J. Talamas, Jay F. Brunner, Kim A. Hoelmer, Matthew L. Buffington, and Elizabeth H. Beers (2016) Discovery of an Exotic Egg Parasitoid of the Brown Marmorated Stink Bug, Halyomorpha halys (Stål) in the Pacific Northwest. Proceedings of the Entomological Society of Washington: Vol. 118, No. 3, pp. 466-470. doi: http://dx.doi.org/10.4289/0013-8797.118.3.466

We report the first known incidence of two parasitoid species of the invasive pest, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), in the United States (US). The discovery of Ganaspis brasiliensis (Ihering) (Hymenoptera: Figitidae) and Leptopilina japonica (Novković & Kimura) (Hymenoptera: Figitidae) in northwestern Washington State (US) was made shortly after their discovery in nearby southwestern British Columbia (Canada), indicating that contiguous populations of these species are established in both countries. The first specimen of L. japonica from Washington was collected in the fall of 2020, when it was found in a rice wine/orange juice trap deployed to survey for Vespa mandarinia Smith (Hymenoptera: Vespidae). Subsequent examination of trap contents from the 2020–2021 seasons indicated the presence of both L. japonica and G. brasiliensis. In September of 2021, live collections of both G. brasiliensis and L. japonica were made, reared from D. suzukii-infested Himalayan blackberry in Whatcom County, WA. Adult parasitoid identifications were based on morphology and COI DNA barcodes. All sequenced specimens to date from Washington and British Columbia belong to the G1 group of G. brasiliensis, the only group approved for release as a classical biological control agent in the US. This study provides an example of how even small changes in the geographic range of a natural enemy, now extending across an international border, may have significant consequences for the future of a biological control program.

In recent years, there has been an increase in the adventive establishment and spread of parasitoid wasps outside of their native range. However, lack of taxonomic tools can hinder the efficient screening of field-collected samples to document the establishment and range expansion of parasitoids on continent-wide geographic scales. Here we report that Leptopilina japonica (Hymenoptera, Figitidae), a parasitoid of the globally invasive fruit pest Drosophila suzukii (Diptera, Drosophilidae), is now widespread in much of North America despite not having been intentionally introduced. Surveys in 2022 using a variety of methods detected L. japonica in 10 of 11 surveyed USA States and one Canadian Province where it was not previously known to occur. In most surveys, L. japonica was the most common species of D. suzukii parasitoid found. The surveys also resulted in the detection of Ganaspis cf. brasiliensis (Hymenoptera, Figitidae), the recently-released biological control agent of D. suzukii, in six USA States where it had not previously been found. These new detections are likely a result of intentional biological control introductions rather than spread of adventive populations. A species-specific multiplex PCR assay was developed as a rapid, accurate and cost-effective method to distinguish L. japonica, G. cf. brasiliensis, the closely-related cosmopolitan parasitoid Leptopilina heterotoma (Hymenoptera, Figitidae) and other native parasitoid species. This dataset and the associated molecular tools will facilitate future studies of the spread and ecological impacts of these introduced parasitoids on multiple continents.

Trissolcus japonicus (Ashmead), an Asian parasitoid of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), was first detected in North America in 2014. Although testing in quarantine facilities as a candidate for classical biological control is ongoing, adventive populations have appeared in multiple sites in the United States, Canada, and Europe. Extensive laboratory testing of T. japonicus against other North American pentatomids and H. halys has revealed a higher rate of parasitism of H. halys, but not complete host specificity. However, laboratory tests are necessarily artificial, in which many host finding and acceptance cues may be circumvented. We offered sentinel egg masses of three native pentatomid (Hemiptera: Pentatomidae) pest species (Chinavia hilaris (Say), Euschistus conspersus Uhler, and Chlorochroa ligata (Say)) in a field paired-host assay in an area with a well-established adventive population of T. japonicus near Vancouver, WA. Overall, 67% of the H. halys egg masses were parasitized by T. japonicus during the 2-yr study. Despite the ‘worst case’ scenario for a field test (close proximity of the paired egg masses), the rate of parasitism (% eggs producing adult wasps) on all three native species was significantly less (0.4–8%) than that on H. halys eggs (77%). The levels of successful parasitism of T. japonicus of the three species are C. hilaris > E. conspersus > C. ligata. The potential impact of T. japonicus on these pentatomids is probably minimal.

The effects of three sulfur products (calcium polysulfide [= lime sulfur], dry flowable sulfur, and ammonium thiosulfate, a plant nutrient), were tes