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

Habitat and vertical stratification affect capture of stink bugs (Hemiptera: Pentatomidae) and biological control of the invasive brown marmorated stink bug

Spatiotemporal distribution of stink bugs (Hemiptera: Pentatomidae) and their natural enemies across farmscapes has been studied in more detail recently. However, the impact of plant height on vertical stratification of stink bugs and their natural enemies is rarely addressed across these diverse habitats. In this study, we examined capture of native stink bugs, the invasive brown marmorated stink bug, Halyomorpha halys (Stål)(Hemiptera:Pentatomidae), and a predaceous wasp, Astata occidentalis Cresson (Hymenoptera: Sphecidae) in pheromone-baited traps, in 2 habitats, woodlands of mostly deciduous trees mixed with some conifers and pecan orchards, in addition to their vertical stratification (0-13.7 m) at increasing heights. Furthermore, the effects of canopy height and habitat on H. halys egg mass predation and parasitism were evaluated. Adult H. halys were abundant in both habitats, but more nymphs were captured in pecan orchards. The same pattern was found for adult Euschistus servus (Say) (Hemiptera:Pentatomidae), Thyanta custator McAtee (Hemiptera:Pentatomidae), and A. occidentalis. In contrast, adult E. tristigmus (Say) (Hemiptera:Pentatomidae) and Chinavia hilaris (Say) (Hemiptera:Pentatomidae) were more abundant in woodlands. More nymphal H. halys and adults of E. servus, T. custator, and A. occidentalis were captured in ground traps than canopy traps in pecan. More adult and nymphal H. halys were captured at varying heights in the woodland canopy compared to near the ground as were adult E. tristigmus and C. hilaris. Both parasitism and predation occurred in woodland and pecan canopies. However, in one test we found that parasitism of H. halys egg masses occurred more often in the upper tree canopy, and more parasitism was detected in woodland than orchard habitat. In 2 tests, predation was higher in woodlands than pecan orchards. These results will aid in optimizing conservation biological control tactics in these habitats.

Predation and parasitism of naturally occurring and sentinel stink bug egg masses of Halyomorpha halys (Stål) and Nezara viridula (L.) (Hemiptera: Pentatomidae) in various southeastern habitats

Stink bugs, including Halyomorpha halys (Stål) and Nezara viridula (L.), are agricultural pests that feed on fruit in a variety of crops. Monitoring predation and parasitism of stink bug egg masses furthers our understanding of potential biological control tactics. However, best practices for laboratory and field assessments of parasitism and predation of egg masses require further attention. We carried out a series of laboratory and field experiments to test whether parasitism and predation for three types of sentinel H. halys egg masses, fresh, frozen, and refrigerated, varied in agricultural commodities. In addition, we asked if predation and parasitism differed between sentinel and naturally occurring H. halys and N. viridula egg masses in soybean. In the laboratory, more H. halys eggs were parasitized by Trissolcus euschisti (Ashmead) (Hymenoptera: Scelionidae) if they were frozen or refrigerated compared to fresh eggs. Similarly, in the field, parasitism was higher for frozen egg masses than fresh. In 2018 and 2019, H. halys natural egg masses had higher parasitism and lower predation compared to sentinel egg masses in soybean. In a paired field test during 2020 and 2021, there was no difference in parasitism between H. halys natural and sentinel eggs, but much higher incidence of parasitism was detected in natural N. viridula egg masses than sentinel eggs. Collecting natural egg masses is the best methodology for field assessment of parasitism of stink bug egg masses; however, if natural egg masses are not easily available, deploying refrigerated sentinel egg masses is a good alternative.

Evaluating Chemical Cues Associated with Halyomorpha halys Toward Enhanced Sensitivity of Surveillance for Trissolcus japonicus

In Asia, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is the predominant egg parasitoid of the brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). Detections of adventive T. japonicus populations in North America since 2014, where invasive H. halys populations have impacted various specialty crops, spurred surveillance efforts to track T. japonicus, and yellow sticky cards (YSC) deployed in H. halys host trees have proven effective for this purpose. While T. japonicus exhibits positive behavioral responses to several olfactory stimuli associated with H. halys under laboratory conditions, these have not been evaluated for their potential utility to enhance surveillance of T. japonicus in the field. In northwestern Virginia, where both H. halys and T. japonicus are well-established, we examined the effect of baiting tree of heaven, Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae), with lures containing the H. halys aggregation pheromone and pheromone synergist on the abundance of H. halys egg masses and captures of T. japonicus in YSC. We also assessed the effect of baiting YSC with newly-laid H. halys egg masses or n-tridecane, a component of H. halys tarsal prints, on T. japonicus captures. Destructive sampling of pheromone-baited and nonbaited trees revealed no significant differences in H. halys egg mass abundance on foliage. Similarly, YSC deployed in pheromone-baited and nonbaited trees showed no significant differences in T. japonicus captures. Moreover, YSC augmented with H. halys egg masses or n-tridecane showed no increase in T. japonicus captures compared with nonbaited controls. The implications for surveillance of adventive T. japonicus are discussed.

Influence of Trap Location in the Tree Canopy on Captures of Adventive Trissolcus japonicus (Hymenoptera: Scelionidae)

Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is an egg parasitoid of the invasive Asian pest, brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). Also native to Asia, adventive T. japonicus populations have been detected in North America since 2014, and are currently reported from 15 U.S. states, the District of Columbia, and two Canadian provinces. Yellow sticky cards (YSC) have proven effective for monitoring the presence, seasonal abundance, and distribution of these adventive populations. Our research has utilized YSC deployed in the midcanopy of H. halys host trees, following a study in which all leaves on felled tree of heaven, Ailanthus altissima (Mill.) Swingle, were inspected for H. halys egg masses, yielding eggs parasitized by T. japonicus only from mid- and upper-canopy leaves. However, given that other investigators have captured T. japonicus using YSC deployed in the lower-canopy, and that the effect of YSC placement in trees on T. japonicus captures had not been examined, captures of T. japonicus on YSC in the mid- and lower-canopy of individual A. altissima were compared. Traps were replaced weekly for five weeks and assessed for scelionid species. In 2020 and 2021, T. japonicus represented ≥53% of all Scelionidae captured, and there was not a significant effect of YSC location in the canopy on its captures. Deploying YSC at either canopy height was effective for measuring the relative abundance of T. japonicus, but sampling from the lower canopy substantially improved the efficiency and convenience of T. japonicus surveillance.

Influence of Holding Conditions and Storage Duration of Halyomorpha halys (Hemiptera: Pentatomidae) Eggs on Adventive and Quarantine Populations of Trissolcus japonicus (Hymenoptera: Scelionidae) Behavior and Parasitism Success

Halyomorpha halys (Stål) is an invasive pest in the United States and other countries. In its native range, H. halys eggs are parasitized by a co-evolved parasitoid, Trissolcus japonicus (Ashmead). In the United States, T. japonicus, a classical biological control candidate, is being redistributed in many states where adventive populations exist. To establish if H. halys egg holding conditions affect T. japonicus foraging behavior or successful parasitism, naïve, female parasitoids from an adventive population were allowed to forage in laboratory bioassay arenas with either fresh or frozen (-20 or -80°C) egg masses, the latter held for five durations ranging from 1 h to 112 d. Parasitoid movements were recorded for 1 h. Thereafter, parasitoids were transferred with the same egg mass for 23 h. Additionally, female parasitoids from a quarantine colony were exposed to: 1) pairs of fresh egg masses and egg masses frozen at -40°C (>24 h) or 2) a single fresh egg mass or egg mass frozen at -40°C (<1 h). All exposed egg masses were held to assess progeny emergence. In the foraging bioassay, holding temperature and storage duration appeared to influence host-finding and host quality. Egg masses held at -80°C and fresh egg masses resulted in significantly greater levels of parasitism and progeny emergence compared with eggs held at -20°C. No differences were recorded between egg masses held at -40°C for ≤1 h and fresh egg masses. These results will help refine methods for preparation of egg masses for sentinel monitoring and parasitoid mass rearing protocols.

Seasonal Abundance and Diversity of Egg Parasitoids of Halyomorpha halys in Kiwifruit Orchards in China

To develop effective and targeted biocontrol tactics for the brown marmorated stink bug, Halyomorpha halys, in crop habitats, a good understanding is essential of the abundance and diversity of its parasitoids in different crop habitats in its native range. To obtain information on the egg parasitoid communities of H. halys in kiwifruit, surveys using sentinel egg masses were conducted in 2018 and 2019. These assessed the species composition of egg parasitoids of H. halys in green-fleshed 'Hayward' kiwifruit orchards, and quantified their season-long abundances in orchards under two different management systems. Parasitism was observed from June to August 2018 (mean parasitism: 48%) and from May to August 2019 (mean parasitism: 29%) across the experimental orchards. In total, five different parasitoid species were found across the two surveys seasons in the kiwifruit orchards, Trissolcus japonicus, T. cultratus, T. plautiae, Anastatus japonicus, and Acroclisoides sp., where T. japonicus and T. cultratus were the predominant species. Monthly T. japonicus abundance data had a unimodal distribution in 2018, peaking in July. There were two peaks (May-June and August) in the 2019 season. Overall, T. japonicus was significantly more abundant in the organic orchard than the conventionally managed orchard only in 2018, and its monthly abundance differed significantly in the two orchards in the two survey seasons. Results and their implications for future classical biological control for H. halys in kiwifruit are discussed.

Survey for Adventive Populations of the Samurai Wasp, Trissolcus japonicus (Hymenoptera: Scelionidae) in Pennsylvania at Commercial Fruit Orchards and the Surrounding Forest

Simple Summary

Invasive species that are freed of associated natural predators increase in population and disrupt the management plans of growers. The brown marmorated stink bug, Halyomorpha halys, is an invasive species that originated in Asia. A promising management tactic for the species is to release an associated parasitoid, the samurai wasp, Trissolcus japonicus. Populations of the samurai wasp have begun to adventively establish in several regions, including Pennsylvania. In order to monitor and use the species as an alternative management strategy to insecticides, it is imperative to understand the baseline populations during the early establishment phase. The aims of this study were to determine if the samurai wasp is already present in commercial orchards in Pennsylvania, where the brown marmorated stink bug has been present in high numbers since approximately 2010. Native Trissolcus wasps were also identified. This study found the samurai wasp in eight counties in Pennsylvania with several orchards containing populations of the species within orchard blocks. These baseline data provide a starting point for controlling H. halys naturally, which was previously controlled only with broad-spectrum insecticides.

Abstract

The samurai wasp, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), is an egg parasitoid associated with the brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). Trissolcus japonicus is a candidate for classical biological control of H. halys populations. Since 2014, adventive populations of T. japonicus have been detected in 14 US states, in the Canadian provinces of British Columbia and Ontario, and in two European countries, Switzerland and Italy. Establishing baseline information about populations of T. japonicus is important, as this species is not host specific to H. halys and the potential ecological effects of the accidental introductions are not fully known. In this study, yellow sticky cards were deployed at commercial fruit orchards in nine counties in Pennsylvania separated by more than 400 km. Trissolcus japonicus was detected on cards in eight counties, and in two habitats, in the orchard and at the forest border. Other native species of Scelionidae known to attack the eggs of H. halys were also identified, including Trissolcus euschisti (Ashmead), Trissolcus brochymenae (Ashmead), and Telenomus podisi Ashmead (Hymenoptera: Scelionidae). These results are important baseline ecological knowledge for both T. japonicus, which appears to be established in orchards throughout Pennsylvania, and other native Scelionidae.

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

Simple Summary

Trissolcus japonicus, an important natural enemy of brown marmorated stink bug in Asia, was first detected in the USA in 2014. To investigate when and where T. japonicus is found in the field, yellow sticky traps were deployed in the canopy of tree of heaven growing at the edge of small isolated patches, windbreaks, and woodlots in 2018 and 2019. In both years, captures occurred from May to September, with peaks in July and August. Captures of T. japonicus were recorded from all three habitats but were not consistently associated with a particular habit. In 2017 and 2018, T. japonicus captures were compared between tree of heaven paired with several other H. halys host trees growing at the woods edge, and in 2019, captures in tree of heaven, black walnut, and black locust growing in the same windbreaks were compared. Trissolcus japonicus and several native H. halys parasitoids were captured in all hosts, but there was not a consistent effect of host tree species on T. japonicus captures. These results can be used to inform and optimize future surveillance efforts for detecting T. japonicus as it continues to expand its range in the USA.

Abstract

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.

Assemblage of the Egg Parasitoids of the Invasive Stink Bug Halyomorpha halys: Insights on Plant Host Associations

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive alien species and a key agricultural pest. Its native parasitoids (Trissolcus japonicus Ashmead and Tr. mitsukurii Ashmead) have been registered in several countries where H. halys brought dramatic economic losses and where biological control is considered to be the most effective long-term solution. By searching for stink bug egg masses and exposing sentinel egg masses, we monitored the distribution of native and exotic egg parasitoids in Trentino-Alto Adige (Italy), an area where both the host and parasitoids are in expansion. We recorded ten pentatomids, seven parasitoid species, with the first report of Tr. japonicus in this area and a hyperparasitoid. In the assemblage, Anastatus bifasciatus (Geoffroy) and Tr. mitsukurii were the dominant parasitoids, with a different distribution in terms of context and host plants. Sycamore was the host plant where the highest number of naturally laid parasitized egg masses (26%) were recorded. Trissolcus mitsukurii showed the highest parasitism rate, and was often found in apple orchards. The emergence of exotic parasitoids showed a temporal delay compared to native ones. Sequence analysis of 823 bp of the CO1 mitochondrial gene revealed that the recovered Tr. japonicus and Tr. mitsukurii harbored one single haplotype each. These haplotypes were previously found in 2018 in Northern Italy. While sentinel egg masses proved to be very effective in tracking the arrival of exotic Trissolcus species, the collection of stink bug egg masses provided fundamental data on the plant host species. The results lend strong support to the adaptation of exotic Trissolcus species to the environmental conditions of the range of introduction, providing new information on plant host-associations, fundamental for the development of biological control programs.

Comparison and Refinement of Integrated Pest Management Tactics for Halyomorpha halys (Hemiptera: Pentatomidae) Management in Apple Orchards

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) has been managed primarily with broad-spectrum insecticides in orchard systems. Recently, IPM techniques have been developed specifically for managing H. halys in apple orchards to reduce insecticide inputs and take advantage of its perimeter-driven behavior. In 2015 and 2016, we compared these IPM tactics to one another and an untreated control to measure differences in overall crop protection and insecticide inputs. Tactics included trap-based threshold-triggered spray applications, perimeter-based attract-and-kill (AK) trees treated every 7- and 14-d, and perimeter spray applications applied every 7- and 14-d. All plots were monitored with baited black pyramid traps deployed in plot interiors. In both years, mean number of H. halys captured in untreated control plot traps was significantly greater than plots managed using IPM tactics. In 2015, significantly more insecticide applications were made in 7- and 14-d perimeter and AK plots compared with trap-based threshold plots. There was no significant difference in the percentage of injured fruit in plot interiors among IPM tactics; all were significantly lower than the control. In 2016, significantly more insecticide applications were made in 7-d perimeter spray and AK plots compared with all other treatments. Significantly less injury was detected in plot interiors for 7- and 14-d perimeter and trap-based threshold plots compared with the control and 7- and 14-d AK plots. Although all IPM tactics reduced H. halys injury in apples using a trap-based treatment threshold required fewer insecticide inputs and only during brief periods of the season, while all others required season-long maintenance.

Season-Long Monitoring of the Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Throughout the United States Using Commercially Available Traps and Lures

Reliable monitoring of the invasive Halyomorpha halys abundance, phenology and geographic distribution is critical for its management. Halyomorpha halys adult and nymphal captures on clear sticky traps and in black pyramid traps were compared in 18 states across the Great Lakes, Mid-Atlantic, Southeast, Pacific Northwest and Western regions of the United States. Traps were baited with commercial lures containing the H. halys pheromone and synergist, and deployed at field sites bordering agricultural or urban locations with H. halys host plants. Nymphal and adult captures in pyramid traps were greater than those on sticky traps, but captures were positively correlated between the two trap types within each region and during the early-, mid- and late season across all sites. Sites were further classified as having a low, moderate or high relative H. halys density and again showed positive correlations between captures for the two trap types for nymphs and adults. Among regions, the greatest adult captures were recorded in the Southeast and Mid-Atlantic on pyramid and sticky traps, respectively, with lowest captures recorded in the West. Nymphal captures, while lower than adult captures, were greatest in the Southeast and lowest in the West. Nymphal and adult captures were, generally, greatest during July-August and September-October, respectively. Trapping data were compared with available phenological models showing comparable population peaks at most locations. Results demonstrated that sticky traps offer a simpler alternative to pyramid traps, but both can be reliable tools to monitor H. halys in different geographical locations with varying population densities throughout the season.

Establishment in an Introduced Range: Dispersal Capacity and Winter Survival of Trissolcus japonicus, an Adventive Egg Parasitoid

The herbivorous brown marmorated stink bug, Halyomorpha halys, has spread globally, and one of its key parasitoids, Trissolcus japonicus, has recently been detected in the pest's introduced range. For an exotic natural enemy to impact its targeted host in a novel environment, it must disperse, locate hosts, and potentially be redistributed to susceptible sites. Through intentionally releasing T. japonicus across four Oregon eco-regions, we investigated an introduced parasitoid's dispersal capacity in urban sites and in two perennial crops, hazelnut and raspberry. In a second paired field and laboratory study, we investigated T. japonicus survival in different plant materials. Within three days of release, adult T. japonicus located host egg masses at 45% of sites and, one year later, were detected at 40% of release sites. Areas where released wasps survived winter were mostly urban or semi-natural. In commercial crop release experiments, we recovered the highest percentage of wasps in raspberry within 5 m of the release site but found no statistical difference in dispersal distance with some wasps dispersing up to 50 m. Adult parasitoids survived up to 16 weeks outdoors in the winter, with greater survival over time in bark compared to leaf litter. Wasp survival remained above 50% over the course of a simulated winter environment without precipitation. Our work affirms the continuation of H. halys parasitism by T. japonicus in novel environments and provides insight into the high population sizes necessary to survive winter and locate host egg masses the following season.

Sampling Methods for Adventive Trissolcus japonicus (Hymenoptera: Scelionidae) in a Wild Tree Host of Halyomorpha halys (Hemiptera: Pentatomidae)

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive pest that has established in much of the United States. Adventive populations of an effective Asian egg parasitoid of H. halys, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), have been detected in several states, including Virginia, and its geographic range is expanding. Documenting changes in its distribution and abundance have thus become key research priorities. For these specific purposes, surveillance of T. japonicus over large geographic areas using sentinel H. halys egg masses may not be optimally efficient, and examination of alternative sampling tactics is warranted. In 2016, sentinel H. halys egg masses were deployed as vertical transects in the canopy of female Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae) in Virginia. A brief follow-up study in 2016 using yellow sticky traps deployed in the same trees yielded captures of T. japonicus, leading to a comparison of vertical transects of sentinel eggs and yellow sticky traps in 2017. Both methods yielded T. japonicus detections only in the middle and upper tree canopies, whereas other known H. halys parasitoids were detected in the lower, middle, or upper canopies. Based on this information, a method for deploying yellow sticky traps in the middle canopy of H. halys host trees was assessed in 2017, yielding T. japonicus captures. A comparison of estimated time inputs revealed that traps were more efficient than sentinel eggs in this regard. Results are discussed in relation to the utility of each sampling method to address specific questions about the range expansion and ecology of T. japonicus.