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Simple Summary The brown marmorated stink bug Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is native to Northeast Asia, but has become a serious invasive species in North America and Europe, causing major economic damage to crops. Halyomorpha halys has not established itself in Australia, but it has been intercepted several times at the border, therefore future incursions and establishment are likely. There are few control options for this species and biological control may be a useful management method in Australia. This study summarizes the literature on natural enemies of H. halys in its native and invaded ranges and prioritizes potential biological control agents that could be suitable for use in Australia. The results show two egg parasitoid species as the best candidates: Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae). Because T. mitsukurii is already present in Australia, it offers the possibility of biological control that can be implemented rapidly. Abstract The brown marmorated stink bug Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is native to Northeast Asia, but has become a serious invasive species in North America and Europe, causing major damage to crops. While it has not established itself in Australia, it has been intercepted at the border several times, indicating that future incursions and establishment are a case of when, not if. Biological control is one of the few control options for this species and will be important for managing H. halys should it become established in Australia. Prioritizing species that could be used as biological control agents would ensure Australia is prepared. This study summarizes the literature on natural enemies of H. halys in its native and invaded ranges and prioritizes potential biological control agents of H. halys that could be used in Australia. Two egg parasitoid species were identified: Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae). Future efforts to develop biological control should focus on T. mitsukurii, as it is already present in Australia. However, little is known about this species and further work is required to: (1) assess its potential effectiveness in parasitizing H. halys, (2) determine its current distribution and (3) host range in Australia.

The samurai wasp, Trissolcus japonicus (Ashmead), has been proposed as a biocontrol agent against brown marmorated stink bugs (BMSB), due to its ability to parasitize and kill BMSB eggs. However, the wasps’ small size makes it challenging for those untrained in morphological identification to determine the wasps’ species. To circumvent this problem, a molecular method was created to identify T. japonicus. The method uses species-specific primers, designed in this study, which target the variable region of the mitochondrial Cytochrome Oxidase 1 (CO1) locus. After confirming successful DNA extraction from samples, the PCR amplification using our primers produced 227-bp PCR products for all T. japonicus specimens and no amplification in other microhymenoptera candidates. Additionally, DNA from BMSB-parasitized eggs gave positive PCR amplification, while the control BMSB samples showed no amplification. This indicates that PCR with our primers specifically and sensitively differentiates T. japonicus specimens from other similar wasp species and discriminates between T. japonicus-parasitized and non-parasitized BMSB eggs. Finally, an in silico analysis of CO1 sequences demonstrated that our primers match the sequences of four different haplotypes of T. japonicus, indicating that our diagnostic method could potentially be applied to analyze T. japonicus populations throughout North America, Europe, and parts of Asia.