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

Mathematical modeling of the parasitism and hyperparasitism increase on Halyomorpha halys eggs in a five-year survey in Northern Italy

The invasive stink bug Halyomorpha halys has become an important pest of many crops, causing severe economic losses to farmers. Control of the pest mainly relies on multiple applications of broad-spectrum insecticides, undermining the integrated pest management programs and causing secondary pest outbreaks. In the native area, egg parasitoids are the main natural enemies of H. halys, among which Trissolcus japonicus is considered the predominant species. In Italy, adventive populations of T. japonicus and Trissolcus mitsukurii, another egg parasitoid of H. halys in Japan, have established themselves. These two species, together with the indigenous Anastatus bifasciatus, are capable of attacking the eggs of the exotic host. Focusing on the situation in Northern Italy, where also the hyperparasitoid Acroclisoides sinicus is present, a discrete-time model is developed for the simulation of the pest evolution. It is based on actual field data collected over a timespan of five years. The simulations indicate that egg parasitoid by themselves do not suppress populations to non-pest levels, but can play an important role in reducing their impact. Both the data from the five-year surveys and those available in the literature are used in the model. It has some limitations in the fact that climatic conditions were not considered, while more accurate simulations could be performed with additional collection of field data, which at the moment are based on partial field observations not sampled at the same sites.

How do outside-hosts-overwintering parasitoids, at the adult stage, cope with cold?

INTRODUCTION

When overwintering, most endoparasitoids are protected from the cold inside their hosts. However, some endoparasitoids, along with ectoparasitoids, fall into the category called outside-hosts-overwintering parasitoids (OHOP) at immature or adult stages. We compared the cold-hardiness capacity and strategy between adult OHOP and their hosts (HOST) by examining their supercooling points (SCP), with acclimation periods and acclimation temperatures, and their lower lethal temperatures at 50% mortality (LLT50). We hypothesized that OHOP are more cold-hardy than their HOST, with lower SCP and LLT50.

MATERIALS AND METHODS

Throughout the summers of 2020, 2021, and 2022, adult cabbage seedpod weevils (HOST) were sampled with a sweep net at the canola pod stage, and thousands of pods were collected and placed in emergence boxes to retrieve the adult OHOP Trichomalus perfectus. Regarding SCP measures, OHOP and HOST were separated according to various treatments. Each treatment considered a target exposure temperature (5, 10, or 20 °C) or a target exposure period (5, 15 or 25 days) at 5 °C. Regarding LLT measures, OHOP and HOST were categorized into five treatments, each corresponding to a specific exposure temperature (-5, -10, -15, -20 or -25 °C).

RESULTS AND CONCLUSION

Acclimations to a lower temperature (5 °C) and a longer period (25 days) led to a significantly lower SCP of OHOP than HOST. Regarding OHOP, the average SCP was -19.71 °C when the acclimation temperature was 20 °C and significantly decreased to -23.20 °C when it was 5 °C. The average SCP was -18.82 °C when the acclimation period was five days and significantly decreased to -23.20 °C when it was 25 days. Conversely, the average SCP for HOST was never below -20 °C. At 20 °C acclimation temperature, HOST exhibited a significantly higher SCP of -14.64 °C compared to acclimations at 5 °C (-19.19 °C) and 10 °C (-20.00 °C), but there were no significant differences between 5 and 10 °C nor between acclimation periods. Therefore, the adult OHOP is more cold-hardy than its HOST. OHOP also exhibited a lower LLT50 than HOST, with -19.20 °C versus -17.59 °C. Finally, OHOP and HOST employ the same freeze-avoidance strategy, as evidenced by their SCP values (-19.57 °C versus -16.80 °C) which closely align with their respective LLT50. Adult OHOP better survive winter than their HOST in cold environments.

An Effective Fluorescent Marker for Tracking the Dispersal of Small Insects with Field Evidence of Mark-Release-Recapture of Trissolcus japonicus

Understanding insect dispersal helps us predict the spread of insect pests and their natural enemies. Dispersal can be studied by marking, releasing, and recapturing insects, known as mark-release-recapture (MRR). MRR techniques should be convenient, economical, and persistent. Currently, there are limited options for marking small parasitoids that do not impact their fitness and dispersal ability. We evaluated commercially available fluorescent markers used in forensics. These fluorophores can easily be detected by ultraviolet (UV) light, requiring minimal costs and labor to process the marked specimens. This fluorophore marking technique was evaluated with the pest Drosophila suzukii and three parasitoids: Trissolcus japonicus, Pachycrepoideus vindemiae, Ganaspis brasiliensis (=G. kimorum). We evaluated the persistence of the marks on all the insects over time and examined the parasitoids for impacts on longevity, parasitism, locomotor activity, and flight take-off. The green fluorophore marker persisted for over 20 days on all four species. Marking generally did not consistently reduce the survival, parasitism rate, locomotor activity, or take-off of the parasitoids tested. Marked T. japonicus were recaptured in the field up to 100 m away from the release point and three weeks after release, indicating that this technique is a viable method for studying parasitoid dispersal.

Releasing and tracking the distribution of adventive Trissolcus japonicus (Hymenoptera: Scelionidae) in Virginia

Adventive populations of Trissolcus japonicus (Ashmead), an egg parasitoid of the invasive agricultural pest, brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), have been detected in the United States since 2014. Given its importance as an H. halys biocontrol agent, efforts to redistribute T. japonicus began within some US states. Our surveillance for T. japonicus in northwestern Virginia in 2016-2017 yielded annual detections only in 1 county. Thus, to promote its broader establishment, releases of H. halys egg masses parasitized by T. japonicus from Virginia occurred in 2018 (2 releases) and 2020 (1 release) at 9 sites throughout Virginia's tree fruit production regions. Monitoring of T. japonicus and H. halys, using yellow sticky cards deployed in H. halys host trees and pheromone-baited sticky traps, respectively, was conducted from 2018 to 2022. Annual captures of H. halys adults and nymphs appeared to reflect adequate populations to support T. japonicus establishment across most or all sites. Prerelease monitoring yielded a single T. japonicus at 1 site. By 2022, T. japonicus was detected at or near 7 of the remaining 8 release sites, with first detections varying between 1 and 2 yr from the releases in 2018 and 2020. Captures at most sites were very low, but establishment at several locations was indicated by detections in 2-4 seasons. In 2022, T. japonicus surveillance at 11 additional sites in northwestern Virginia yielded detections at all locations, including those at which it had not been detected in 2016-2017, providing evidence for its range expansion.

Combining Irradiation and Biological Control against Brown Marmorated Stink Bug: Are Sterile Eggs a Suitable Substrate for the Egg Parasitoid Trissolcus japonicus?

The brown marmorated stink bug (BMSB), Halyomorpha halys, is a phytophagous invasive pest native to south-eastern Asia, and it is now distributed worldwide. This species is considered to be one of the most damaging insect pests in North America and in Europe. In agriculture, the predominant approach to managing BMSB is based on the use of insecticides, specifically pyrethroids and neonicotinoids. Unfortunately, the biology of the species and its facility to develop mechanisms of resistance to available pesticides has induced farmers and scientists to develop different, least-toxic, and more effective strategies of control. In a territorial area-wide approach, the use of a classical biological control program in combination with other least-toxic strategies has been given prominent consideration. Following exploratory surveys in the native range, attention has focused on Trissolcus japonicus, a small scelionid egg parasitoid wasp that is able to oviposit and complete its larval development in a single egg of H. halys. A common method for detecting egg parasitoids in the native range involves the placement of so-called 'sentinel' egg masses of the pest in the environment for a short period, which are then returned to the laboratory to determine if any of them are parasitized. Outside of the area of origin, the use of fertile sentinel eggs of the alien species may lead to the further release of the pest species; an alternative is to use sterile sentinel eggs to record the presence of new indigenous egg parasitoids or to detect the dispersal of alien species (in this case, T. japonicus) released in a new environment to control the target insect pest species. This study evaluated the performance of three types of sterile sentinel eggs as a suitable substrate for the oviposition and larval development of the egg parasitoid T. japonicus in a context of combining classical biological control with a Sterile Insect Technique (SIT) approach.

Factors influencing short-term parasitoid establishment and efficacy for the biological control of Halyomorpha halys with the samurai wasp Trissolcus japonicus

BACKGROUND

Classical biological control has been identified as the most promising approach to limit the impact of the invasive pest species Halyomorpha halys (Heteroptera: Pentatomidae). This study investigated the parasitism rate at sites where the biocontrol agent Trissolcus japonicus (Hymenoptera: Scelionidae) was released and where its unintentional introduction took place, in the Trentino-South Tyrol region. The effect of land-use composition was studied to understand which factors favor the establishment of hosts and parasitoids, including native and exotic species.

RESULTS

The released T. japonicus were detected a year after the start of the program, with a significant parasitoid impact and discovery, compared to control sites. Trissolcus japonicus was the most abundant H. halys parasitoid, and Trissolcus mitsukurii and Anastatus bifasciatus were recorded also. The efficacy of T. mitsukurii was lower in sites where T. japonicus was successfully established, suggesting a possible competitive interaction. Parasitism level by T. japonicus at the release sites was 12.5% in 2020 and 16.4% in 2021. The combined effect of predation and parasitization increased H. halys mortality up to 50% at the release sites. Landscape composition analysis showed that both H. halys and T. japonicus were more likely to be found at sites with lower altitude and with permanent crops, whereas other hosts and parasitoids preferred different conditions.

CONCLUSION

Trissolcus japonicus showed a promising impact on H. halys, at release and adventive sites, with minor nontarget effects, mediated by landscape heterogeneity. The prevalence of T. japonicus in landscapes with permanent crops could support IPM in the future. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genetic relationships among laboratory lines of the egg parasitoid Trissolcus japonicus from native and adventive populations

Candidate biological control agents of invasive insect pests are increasingly being found in new geographic regions as a result of unintentional introductions. However, testing the degree of genetic differentiation among adventive and native-range populations of these agents is rarely done. We used reduced-representation sequencing of genomic DNA to investigate the relationships among laboratory lines of Trissolcus japonicus (Ashmead) (Hymenoptera, Scelionidae), an egg parasitoid and biological control agent of the brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera, Pentatomidae). We compared sequences from multiple adventive populations in North America (Canada, USA) and Europe (Switzerland) with populations sourced from part of its native range in China. We found considerably more genetic variation among lines sourced from adventive populations than among those within native populations. In the Pacific Northwest of North America (British Columbia, Canada and Washington State, USA), we found preliminary evidence of three distinct genetic clusters, two of which were highly dissimilar from all other lines we genotyped. In contrast, we found that other adventive lines with close geographic proximity (two from Ontario, Canada, three from Switzerland) had limited genetic variation. These findings provide a basis for testing biological differences among lines that will inform their use as biological control agents, and provide evidence to support a hypothesis of several independent introductions of T. japonicus in western North America from different source areas.

Performance of two egg parasitoids of brown marmorated stink bug before and after cold storage

Introduction: The genus Trissolcus includes a number of egg parasitoids that are known to contribute to the control of Halyomorpha halys. The number of progenies, particularly females, is important for the efficient mass rearing of species used in augmentative biological control programs. Cold storage is an important technique for extending the shelf life of natural enemies used in such programs. Methods: We assessed how fecundity, sex ratio, lifespan, and the number of hosts parasitized within 24 h were affected by host density for T. japonicus and T. cultratus when offered fresh H. halys eggs and how these parameters were affected if adult parasitoids were first placed in cold storage (11°C in the dark) for 19 weeks before being used for propagation. Results: The fecundity were 110.2 and 84.2 offspring emerged at 25°C, for parasitoids not placed in cold storage; among the offspring that emerged, 82.6% and 85.6% were female for T. japonicus and T. cultratus, respectively. If first placed in cold storage, T. japonicus and T. cultratus produced 35.1 and 24.6 offspring per female, respectively, although cold storage significantly extended the shelf life. The survival rates of parasitoids that were placed in cold storage were 90.3% and 81.3% for females, and 3.2% and 0.9% for males of T. japonicus and T. cultratus, respectively. The number of hosts parasitized within 24 h was not shown to be density dependent, but it was significantly lower after cold storage. Discussion: This information can be used to estimate the likely production for augmented rearing colonies for use in biological control programs.

Comparison of Yellow and Blue Sticky Cards for Detection and Monitoring Parasitoid Wasps of the Invasive Halyomorpha halys (Hemiptera: Pentatomidae)

The invasive Halyomorpha halys (Stål) is a significant agricultural and urban nuisance pest in many parts of the world. In North America, biological control of H. halys by parasitoid wasps in the families Scelionidae and Eupelmidae has shown promise. An effective technique for detection and monitoring native and exotic parasitoids is the deployment of yellow sticky cards; however, yellow cards also attract nontarget arthropods, reducing efficiency and accuracy of parasitoid screening. This study sought to identify an alternative yet effective trapping technique by comparing the number of target parasitoid wasps [Anastatus spp. Motschulsky (Hymenoptera: Eupelmidae), Telenomus spp. Haliday (Hymenoptera: Scelionidae), and Trissolcus spp. Ashmead (Hymenoptera: Scelionidae)] and arthropod bycatch on yellow and blue sticky cards deployed in urban, orchard, and vegetable landscapes in northern Utah from late May to early October in 2019 and 2020. Yellow sticky cards captured 54-72% more target parasitoids than blue cards from June through August in all three landscape types in both years; however, a positive correlation in parasitoid capture indicated blue cards detect target parasitoids, just in fewer numbers. Both card colors detected adventive Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) in initial findings of 2019, and in expanded locations of 2020. Furthermore, blue cards captured 31-48% less Diptera and nontarget Hymenoptera than yellow cards in both years across all three landscapes, translating to reduced card processing time and impacts to beneficial insect populations. Our results suggest that blue vs yellow sticky cards offer an alternative monitoring technique to survey for H. halys parasitoids.

Halyomorpha halys (Hemiptera: Pentatomidae) on Kiwifruit in Northern Italy: Phenology, Infestation, and Natural Enemies Assessment

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is an Asian invasive plant-feeding insect and an emerging kiwifruit pest. Knowledge about the BMSB dynamics and damage to kiwifruit outside the bug native range is scarce. This 2-yr study was aimed at describing phenology and infestation dynamics of BMSB in green-fleshed and yellow-fleshed kiwifruits. Natural enemies were investigated as well. Field surveys were performed weekly in two sites in Northern Italy by pheromone-baited traps and visual samplings, from early Spring to mid-Autumn. All BMSB life stages were collected and kept under observation to assess occurrence of parasitoids. A sample of fruit was dissected weekly to detect BMSB feeding injuries. In 2018-2019, BMSB was found throughout the growing season with two generations per year with a large overlapping of all life stages. Pheromone-baited traps and visual samplings gave consistent results and can be both considered effective sampling methods on kiwifruit. Fruit injuries were significantly related to kiwifruit development stage, weekly captures of BMSBs by traps, and cultivar. Several BMSB egg masses were found on kiwifruit leaves. Anastatus bifasciatus Geoffroy (Hymenoptera: Eupelmidae), a native egg parasitoid with Palearctic distribution, emerged from 20.14% of eggs in 2018, but the percent parasitism dropped to 0.47% in 2019. In both years, other natural enemies were found exerting negligible pressure on BMSB populations. The determination of reliable economic thresholds for BMSB on kiwifruit is urgently needed to develop a robust and sustainable integrated pest management (IPM) strategy, and this study provides data towards that direction.

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.

Laboratory and field studies supporting augmentation biological control of oriental fruit moth, Grapholita molesta (Lepidoptera: Tortricidae), using Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae)

BACKGROUND

Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae) is a cosmopolitan pests of fruit trees in temperate regions. Control of G. molesta is challenging because larvae feed in concealed locations and have evolved resistance to many pesticides. We compared three commercially available species of Trichogramma for efficacy against G. molesta in the laboratory assays and tested releases of the promising species in a pear orchard.

RESULTS

Laboratory assays indicated that Trichogramma dendrolimi parasitized G. molesta at the highest rate. Parasitoids took longer to oviposit in older host eggs, and fewer eggs were parasitized when they were more than 3 days old. Field tests produced ca 60% cumulative parasitism of sentinel G. molesta eggs with one release of Trichogramma dendrolimi, with most parasitism occurring within 24 h. Female wasps dispersed up to 12 m from release points with a bias toward upwind movement.

CONCLUSION

We calculated that, for each generation of G. molesta, 900 000 wasps per hectare, in three releases 3 days apart, each distributed among release points 10 m apart, would reduce fruit damage by half in an orchard where 50% of fruit would otherwise be damaged. Although augmentation of Trichogramma dendrolimi is a viable tactic for reducing G. molesta populations and fruit damage, it will require integration with other compatible control tactics in order to provide commercially acceptable levels of control in orchards experiencing significant pest pressure. © 2021 Society of Chemical Industry.

Native and Non-Native Egg Parasitoids Associated with Brown Marmorated Stink Bug (Halyomorpha halys [Stål, 1855]; Hemiptera: Pentatomidae) in Western Slovenia

Halyomorpha halys (Hemiptera: Pentatomidae), native to East Asia, has become a globally invasive pest, as a serious threat to agricultural production and a notorious nuisance pest in urban areas. Considerable efforts have been made so far to develop effective pest control measures to prevent crop damage. Biological control of this invasive stink bug by egg parasitoids has proven to be the most environmentally sustainable long-term solution. Knowledge of the native egg parasitoid fauna is of key importance when implementing a biological control program. Therefore, the main objective of our study was to detect egg parasitoid species associated with H. halys in the Goriška region (Western Slovenia) and to evaluate their impact on the pest population under field conditions. In the years 2019 and 2020, around 4600 H. halys eggs were collected in the wild and more than 3400 sentinel eggs were exposed to detect parasitoids in the field. Five egg-parasitoid species emerged from H. halys eggs: Anastatus bifasciatus (Hymenoptera: Eupelmidae), Telenomus sp., Trissolcus basalis, Trissolcus mitsukurii&nbsp;(Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Hymenoptera: Encyrtidae), all of them are new records for Slovenia. The native species, An. bifasciatus, dominated in urban and suburban areas, while non-native Tr. mitsukurii prevailed in agricultural areas.&nbsp;Overall parasitism rates of naturally laid eggs by the parasitoid species complex in 2019 and 2020 was 3.0 and 14.4%, respectively. Rapid recruitment of native parasitoids, early detection of an effective alien parasitoid species and increasing overall parasitism rates are very encouraging results, which need to be followed and verified in future research.

Add Germany to the List-Adventive Population of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) Emerges in Germany

Simple Summary

The brown marmorated stink bug, Halyomorpha halys, is an invasive pest species of global economic importance. It has a very broad host range and causes severe damages in agricultural, horticultural, and fruit crops. Control measures, including available chemical and mechanical options, have often proved insufficient. Surveys of natural enemies in the newly invaded areas have also shown that natural biological control is generally too low to control H. halys populations in the long run. In its native Asian range, egg parasitoids in the genus Trissolcus play an important role in controlling H. halys. Since the mid-2010s, adventive populations of Trissolcus japonicus, a dominant egg parasitoid of H. halys in Asia with a narrow host range, have been reported from several countries with prior establishment of H. halys. Here, we report the first discovery of T. japonicus in Germany. This finding corroborates a northbound expansion of the range of T. japonicus in Europe, along with H. halys.

Abstract

The brown marmorated stink bug, Halyomorpha halys, is a polyphagous pest species of worldwide economic importance. Since the mid-1990s, it has invaded and become established in various countries outside its native Asian range. In the newly invaded areas, biological control by native natural enemies has been shown to be insufficient in the long-term control of this severe pest. Adventive populations of Trissolcus japonicus, an important biological control agent of H. halys in Asia, have been reported from North America and some European countries since the mid-2010s. This egg parasitoid species seems to follow in the wake of the establishment of H. halys populations outside their native Asian range. Here, we report the first discovery of an adventive population of T. japonicus in Germany. In 2020, adult T. japonicus were recovered from parasitized H. halys egg masses (naturally laid and sentinel egg masses) and collected in ruderal areas using an insect suction sampler. The arrival of T. japonicus in Germany, unintentional through pathways yet unknown, corroborates a northbound expansion of its range within Europe. Further field surveys will show the extent of its dispersal and establishment capacities within this new distribution area.

Parasitism and Predation on Sentinel Egg Masses of Three Stink Bug Species (Hemiptera: Pentatomidae) in Native and Exotic Ornamental Landscapes

This study evaluated parasitism and predation on sentinel egg masses of three stink bug species, the spined soldier bug, Podisus maculiventris (Say), the brown stink bug, Euschistus servus (Say), and the invasive brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), in ornamental landscapes composed of either native or exotic plants. This study also compared the species composition of parasitoids attacking two native stink bug species (P. maculiventris and E. servus) with those attacking the invasive BMSB on the same tree species in the same habitat. Overall, egg parasitism and predation were much higher on the two native stink bug species compared with BMSB, with an average parasitism rate of 20.6% for E. servus, 12.7% for P. maculiventris, and only 4.2% for H. halys and an average predation rate of 8.2% for E. servus,17.7% for P. maculiventris, and 2.3% for H. halys. Egg predation was also significantly higher on P. maculiventris than on E. servus eggs. Eight parasitoid species attacked sentinel stink bug eggs in the ornamental landscaped plots. Trissolcus euschisti (Ashmead) (Hymenoptera: Scelionidae) was the predominant parasitoid for all three stink bug species. There were no significant differences in parasitism and predation rates on any of the stink bug species between native and exotic plots. Therefore, there is no evidence that ornamental landscapes composed of native plants increased parasitism or predation rates of sentinel egg masses of two native stink bug species or the invasive BMSB, compared with those composed entirely of exotic plants.

An Effective Cold Storage Method for Stockpiling Halyomorpha halys (Hemiptera: Pentatomidae) Eggs for Field Surveys and Laboratory Rearing of Trissolcus japonicus (Hymenoptera: Scelionidae)

An effective stockpiling method for egg masses of the invasive brown marmorated stink bug (Halyomorpha halys [Stål]; Hemiptera: Pentatomidae) would be useful for rearing and field studies of its egg parasitoid Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae). The current method of stockpiling H. halys egg masses at subzero temperatures has lethal and sublethal fitness consequences for T. japonicus. Our goal was to test the efficacy of refrigeration as an alternative method for stockpiling H. halys eggs. We show that parasitoid emergence from egg masses refrigerated at 8°C for up to two months before parasitism is higher than from frozen egg masses. In addition, 8°C cold storage usually had minimal or no sublethal fitness effects on emerging T. japonicus. Only after two months of host egg refrigeration did the emergence of T. japonicus begin to decrease significantly (by ~10% relative to untreated viable egg masses), whereas egg masses previously frozen at -80°C had a ~59% reduction in parasitoid emergence after 14 d of storage. Refrigerated egg masses that were subsequently exposed to a range of field-realistic average temperatures were still suitable for T. japonicus parasitism after 7 d. Our results demonstrate that refrigeration at 8°C, while resulting in complete mortality of H. halys embryos after 10 d, are more suitable for T. japonicus parasitism than those stored at -80°C. The quantity and quality of H. halys eggs that can be stockpiled with this method could facilitate T. japonicus laboratory colony maintenance, field monitoring, and releases.

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.

Surveys in northern Utah for egg parasitoids of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) detect Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae)

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.