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The highly polyphagous and invasive brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), has become a significant insect pest in North America since its detection in 1996. It was first documented in northern Utah in 2012 and reports of urban nuisance problems and plant damage have since increased. Biological control is the preferred solution to managing H. halys in North America and other invaded regions due to its alignment with integrated pest management and sustainable practices. Native and non-native biological control agents, namely parasitoid wasps, have been assessed for efficacy. Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is an effective egg parasitoid of H. halys in its native range of southeast Asia and has recently been documented parasitising H. halys eggs in North America and Europe. Field surveys for native and exotic egg parasitoids using wild (in situ) and lab-reared H. halys egg masses were conducted in suburban and agricultural sites in northern Utah from June to September 2017–2019. Seven native wasp species in the families Eupelmidae and Scelionidae were discovered guarding H. halys eggs and adult wasps from five of these species completed emergence. Native species had low mean rates of adult emergence from wild (0.5–3.7%) and lab-reared (0–0.4%) egg masses. In 2019, an adventive population of T. japonicus was discovered for the first time in Utah, emerging from 21 of the 106 wild H. halys egg masses found that year, and none from lab-reared eggs. All T. japonicus emerged from egg masses collected on Catalpa speciosa (Warder). Our results support other studies that have observed biological control of H. halys from T. japonicus and improved parasitoid wasp detection with wild as compared to lab-reared H. halys egg masses.

Halyomorpha halys is a severe invasive Asian pest worldwide and classical biological control is foreseen as the most promising control method. Egg parasitoids appear to be the most important natural enemies of this pest, especially the Asian hymenopteran Trissolcus japonicus. In the invaded areas, only a few egg parasitoid species have been able to adopt H. halys as a host. Anastatus bifasciatus is the most common native egg parasitoid of H. halys in Europe, but reaches only low levels of parasitization, while several other native species are only occasionally found. Recently, adventive populations have been found both in the USA and in Europe of T. japonicus, and in Italy of a second Asian species, Trissolcus mitsukurii. Species identification based on morphological traits by specialists or by molecular analysis is a crucial step in the management of biological control programs. The ability to identify the genus or species within a narrow guild of egg parasitoids based on adult emergence holes and meconium features can be a simple and useful method to support management efforts. We present here detailed descriptions of the meconium of the most frequent parasitoid species attacking H. halys in Europe and the characteristics of their emergence holes of the adult wasps.

As the brown marmorated stink bug (Halyomorpha halys) has spread across the Northern Hemisphere, research on its egg parasitoids has increased accordingly. These studies have included species-level taxonomy, experimental assessments of host ranges in quarantine, and surveys to assess parasitism in the field. We here present a molecular phylogeny of Trissolcus that includes all species that have been reared from live H. halys eggs. Species-group concepts are discussed and revised in the light of the phylogenetic analyses. The analyses indicate that the ability to successfully parasitize H. halys eggs is not phylogenetically constrained, but the most effective parasitoids are all found in the flavipes species group.

The invasive and highly polyphagous brown marmorated stink bug, Halyomorpha halys (Stål), is a severe agricultural and urban nuisance pest in North America. Since its initial invasion into Utah in 2012, H. halys has become well established in urban and suburban locations along the western foothills of the Wasatch Front in northern Utah. Bordering the Great Basin Desert, this area is unique from other North American locations with H. halys due to its high elevation (> 1200 m), aridity (30-year mean RH = 53.1%; dew point = -1.9 °C) and extreme temperatures (the 30-year mean minimum and maximum in January and July in Salt Lake City range from -3.1 to 3.6 °C and 20.3 to 32.4 °C, respectively). To document which plant species harbour H. halys, surveys were conducted in 17 urban/suburban sites in four counties during 2017 and 2018. Halyomorpha halys was more abundant in Salt Lake and Utah counties than in the more northern counties of Davis and Weber and was found on 53 plant species, nine of which hosted two or more developmental stages in both years. The majority of hosts were in the families Fabaceae, Rosaceae and Sapindaceae. Northern catalpa, Catalpa speciosa (Warder), was the most consistent host, supporting a majority of H. halys detections in all life stages; thus we identify it as a sentinel host. Twenty-nine species were novel hosts for H. halys in North America; of these, Acer ginnala Maxim, Populus tremuloides Michx., Prunus armeniaca × domestica ‘Flavor King’ and Prunus virginiana ‘Schubert’ were detected with two or more life stages of H. halys in both years. Peak populations of H. halys occurred from mid-June to mid-September. We describe H. halys plant utilisation by life stage and seasonal period to aid future detection and management of this invasive insect in the greater Intermountain West region.

A parasitoid wasp, Trissolcus basalis (Wollaston), was recorded parasitizing eggs of the invasive stink bug Halyomorpha halys (Stål) in the United States. This is the first record of this species parasitizing fresh and frozen eggs of H. halys in the United States. First record of Trissolcus basalis parasitizing Halyomorpha halys eggs in the United States.