Parasitoid-host association in invaded communities.

In nature, most parasitoids attack more than one host species, and nearly all hosts are attacked by several species of parasitoids. This opens many potential opportunities for interactions of invasive species with native parasitoid-host association networks in invaded communities. Despite this, few studies have examined the direct and indirect impacts of biological invasion on parasitoid-host associations. This review examines what is known of these relationships from the most recent literature and suggests future research priorities. We conclude that parasitoid-host association networks in invaded communities are complex, dynamic, and subject to trophic intrusions from invasive plants, herbivores, plant pathogens, parasitoids, and hyperparasitoids. Future studies should take a holistic systems approach to understanding the impact of biological invasion and its consequences in shaping community structure through altering existing native, coevolved parasitoid-host association networks.

Postrelease assessment of Oobius agrili (Hymenoptera: Encyrtidae) establishment and persistence in Michigan and the Northeastern United States.

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive woodboring pest of ash trees (Fraxinus sp.) in North America. Among the Asiatic parasitoids being released for the management of EAB in North America, Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) is the only EAB egg parasitoid. To date, more than 2.5 million O. agrili have been released in North America; however, few studies have examined its success as a biological control agent of EAB. We conducted studies to assess O. agrili establishment, persistence, spread, and EAB egg parasitism rates in Michigan at the earliest release sites (2007-2010), as well as at more recent release sites (2015-2016) in 3 Northeastern United States (Connecticut, Massachusetts, New York). In both regions, we documented successful O. agrili establishment at all but one release site. In Michigan, O. agrili has persisted at release sites for over a decade and spread to all control sites located 0.6-3.8 km from release sites. Overall, EAB egg parasitism ranged from 1.5% to 51.2% (mean of 21.4%) during 2016-2020 in Michigan and from 2.6% to 29.2% (mean of 16.1%) during 2018-2020 in the Northeastern states. Future research efforts should focus on factors affecting the spatiotemporal variation in EAB egg parasitism rates by O. agrili, as well as its potential range in North America.

Seasonal Captures of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) and the Effects of Habitat Type and Tree Species on Detection Frequency.

Trissolcus japonicus, an important egg parasitoid of Halyomorpha halys in Asia, was first detected in the USA in 2014. To evaluate the effect of habitat and the seasonality of T. japonicus detections in the USA, yellow sticky traps were placed in the canopy of Ailanthus altissima growing at the edge of isolated patches of trees, windbreaks, and woodlots in northern Virginia in 2018 and 2019. In both years, captures occurred from May to September, and peaked in July and August. While T. japonicus was detected in all habitats, there was not a consistent effect of habitat type on capture frequency. To evaluate tree species effects on T. japonicus captures, in 2017 and 2018, yellow sticky traps deployed in the canopy of A. altissima bordering apple orchards were paired with a nearby trap in one of several wild tree species along a common woods edge. In 2019, these traps were deployed in A. altissima, black walnut, and black locust growing in the same windbreaks. No consistent association between captures of T. japonicus or native parasitoids of H. halys and the tree species sampled was observed among years. Results are discussed in relation to the ecology and sampling optimization of T. japonicus.

Vertical Sampling in Tree Canopies for Halyomorpha halys (Hemiptera: Pentatomidae) Life Stages and its Egg Parasitoid, Trissolcus japonicus (Hymenoptera: Scelionidae).

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is an invasive agricultural and nuisance pest that has established across much of the United States and caused significant crop losses in the Mid-Atlantic region. While it has been monitored extensively using ground-deployed pheromone traps, the vertical distribution of its life stages in the canopy of wild tree hosts has not been examined. In Virginia, small pyramid traps baited with 'low-dose' H. halys pheromone lures were deployed via a pulley system at the lower, mid-, and upper canopy of female tree of heaven (Ailanthus altissima (Mill.) Swingle) in 2016 and 2017 and male A. altissima and hackberry (Celtis occidentalis L.) in 2017. Weekly captures of adults and nymphs were recorded throughout each season. Each year, additional female A. altissima trees were felled during the two main periods of H. halys oviposition. The number and relative locations of all pentatomid egg masses found on foliage were recorded and any parasitoids that emerged from them were identified. Halyomorpha halys adults and nymphs were captured in greatest numbers in upper canopy traps and in lowest numbers in traps near the tree base. More H. halys egg masses were collected from mid-canopy than from the lower or upper canopy. The adventive egg parasitoid, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), emerged most frequently from egg masses found at mid-canopy and was not recovered from those in the lower canopy. Results are discussed in relation to the foraging ecology of H. halys and its natural enemies, including TT. japonicus.

Can the Dispersal Behavior of Halyomorpha halys (Hemiptera: Pentatomidae) Inform the Use of Insecticide-Treated Netting to Mitigate Homeowner Issues From its Fall Invasion?

Brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is a serious agricultural pest and can be a significant nuisance when it invades human dwellings during its fall dispersal to overwintering sites. Methods informed by behavioral data to exclude or reduce its entry into buildings are needed. The temporal and spatial distribution of adults on an invaded building was assessed over multiple years, revealing its seasonal dispersal pattern and that its numbers varied by wall aspect. Moreover, its density was higher in recessed doorways than on associated walls, raising questions about its behavioral response to dark, contrasting surfaces. This response was evaluated using black, framed panels of deltamethrin-incorporated netting, non-treated netting, and an open frame with no netting, deployed in pairs on the wall of a private residence. More dispersing adults landed on panels of non-treated netting than on open panels, but there was no difference between panels with treated and non-treated netting. Adults remained on treated panels for less time than on non-treated panels, and most walked rather than flew from both. Adult male and female H. halys collected during the dispersal period were exposed to panels of treated and non-treated netting in a laboratory, using durations derived from field recordings. Exposures to treated panels intoxicated but did not kill them over a 7-d assessment period. The deployment of insecticide-treated netting, guided by the behavior of adult H. halys alighting on buildings, is discussed in relation to potential options to mitigate homeowner issues from this serious annual problem.