An Insight into the Role of Trissolcus mitsukurii as Biological Control Agent of Halyomorpha halys in Northeastern Italy

Assessing the lethal effects of pesticide residue exposure on beneficial parasitoids and their host, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae)

Chemical control is currently the main strategy for managing brown marmorated stink bug, Halyomorpha halys (Stål). However, chemical pesticides can harm nontarget species, including natural enemies of H. halys. Pesticides with high toxicity to H. halys and low toxicity to its parasitoids need to be identified to support H. halys management. This is not only for natural biological control but also for preemptive classical biological control of H. halys by parasitoids. Here, we assessed the contact toxicity of residues of eight insecticides against H. halys and three of its main parasitoid species (Anastatus japonicus Ashmead (Hymenoptera: Eupelmidae), Trissolcus japonicus Ashmead (Hymenoptera: Scelionidae), Trissolcus cultratus Mayr (Hymenoptera: Scelionidae)). This study aims to provide valuable insights for preemptive classical biological control of H. halys using these parasitoids. Our results showed that A. japonicus exhibited higher tolerance to the tested pesticides, while T. japonicus was the most sensitive species. Among the pesticides, chlorantraniliprole had the lowest overall impact on all three parasitoid species. Additionally, acetamiprid, azadirachtin, and rotenone were found to be harmless to A. japonicus. Acetamiprid, however, was slightly harmful to T. cultratus. The remaining pesticides showed moderate to significant harmful effects on the parasitoids. For H. halys adults and fifth instars, the pesticides tested caused no mortality within the 24 h exposure. However, young nymphs were susceptible to the tested pesticides. Fenpropathrin had the highest toxicity to H. halys, killing 83.3%, 52.8%, and 19.4% of second, third, and fourth instars in a 24 h exposure. Fenpropathrin, acetamiprid, cyfluthrin, azadirachtin, and dinotefuran were all slightly harmful to the first instar nymphs. The other pesticides were harmless to H. halys in a 24 h exposure. Halyomorpha halys mortality increased with the contact time with the residue. Mortality of fourth and fifth instars of H. halys was >70% for fenpropathrin, cyfluthrin, dinotefuran, abamectin-aminomethyl, and acetamiprid if exposure continued for 7 d. Acetamiprid was effective in controlling H. halys nymphs but exhibited varying levels of toxicity towards the three tested parasitoid species, depending on the residue age and exposure time. Azadirachtin showed lower overall toxicity to beneficial insects, suggesting that these materials could be used to manage H. halys while minimizing harm to key beneficial species.

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.

Evaluation of an Attract-and-Kill Strategy Using Long-Lasting Insecticide Nets for the Management of the Brown Marmorated Stink Bug in Northern Italy

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is causing extensive economic losses in tree fruit crops. Including attract-and-kill (AK) strategies targeting BMSBs in an integrated pest management framework could reduce the amounts of insecticides sprayed and benefit growers, consumers and the environment. This study evaluated the effectiveness of an area-wide AK strategy across an intensive fruticulture region of Northern Italy, comparing four paired pear sites with and without two AK stations ha-1. These stations consisted of long-lasting insecticide-treated nets containing alpha-cypermethrin, baited with the BMSB aggregation pheromone and synergist. BMSB abundance was estimated using black-standing monitoring traps, and fruit damage upon harvest was recorded across all sites. The AK stations did not decrease the BMSB abundance nor the fruit damage, while after harvest significantly lower BMSB captures were detected in the AK sites compared to the control sites. Whilst the lures' efficacy was corroborated by this research, the killing method requires improvement and refinement.

The First Records of Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) (Hymenoptera, Scelionidae), Alien Egg Parasitoids of Halyomorpha halys (Stål) (Hemiptera, Pentatomidae) in Serbia

Serbia has recently begun facing a serious problem with the Brown Marmorated Stink Bug, Halyomorpha halys (Stål), which was first recorded in October 2015. This species belongs to the Pentomidae family and is notorious for causing extensive damage to plants. During the winter, it tends to gather in urban areas, such as houses and different man-made facilities, which has raised concerns among producers and citizens. The population of this species has rapidly increased, causing significant economic damage to cultivated plants. However, despite the alarming situation no natural enemies have yet been identified in Serbia. Therefore, research in 2022 was focused on collecting stink bug eggs to investigate the presence of egg parasitoids. The study identified two foreign Hymenoptera species for the European region, Trissolcus japonicus (Ashmead) and Tr. mitsukurii (Ashmead) (Scelionidae), recorded for the first time in Serbia. Additionally, the list of egg parasitoid species belonging to the Hymenoptera order includes seven local species: Anastatus bifasciatus (Geoffroy), from the Eupelmidae family; Ooencyrtus sp., from the Encyrtidae family; and Telenomus turesis (Walker), Tr. basalis (Wollaston), Tr. belenus (Walker), Tr. colemani (Crawford), and Tr. semistriatus (Nees von Esenbeck), from the Scelionidae family. In total, nine egg parasitoid species were, for the first time, reported as parasitizing H. halys and related species in Serbia.

Invasion risks presented by Gonopsis affinis and the use of Trissolcus mitsukurii as a biological control agent under present and future climate conditions

BACKGROUND

Gonopsis affinis (Uhler) is a stinkbug that represents a significant threat to the production of rice (Oryza sativa L.), sugarcane (Saccharum officinarum L.) and eulalia (Miscanthus sinensis (Andersson)), and has been listed as a sugarcane pest in Japan. Trissolcus mitsukurii Ashmead is an egg parasitoid of G. affinis. To determine the potential of T. mitsukurii to be a biological control agent for G. affinis, we aim to predict the current and future areas of suitable habitat for these two species and their overlap with areas of present crop production. We developed MaxEnt models using two different variable selection methods and compared the two for T. mitsukurii with a CLIMEX model.

RESULTS

The results showed extensive suitable areas for G. affinis under current climate conditions in East Asia, West Africa, Madagascar, and South America. These ranges overlap with areas currently being used for the production of the three crops in question. More than half overlap with areas of suitable habitat for T. mitsukurii. The most critical environmental variable determining habitat suitability for G. affinis was showed to be precipitation of warmest quarter, whilst for T. mitsukurii it was minimum temperature of the coldest month.

CONCLUSION

Based on our assessment we recommend the immediate implementation of monitoring and invasion prevention measures for G. affinis in southwest China, the Malay Archipelago and West Africa. We suggest that T. mitsukurii be considered for use as a biological control agent in East Asia, Madagascar, Florida and Brazil in the case of future invasions by G. affinis. © 2023 Society of Chemical Industry.

The Introduction and Establishment of Four Invasive Insect Species in Serbia

Urban areas are often populated by specific species of insects, some colorful and appealing, such as ladybugs and butterflies, and others irritating as nuisance bitters or as vectors of pathogens of public health importance. Mosquitoes in urban areas often utilize habitats adjacent to human residences, while phytophagous insect species such as stink bugs often colonize ornamental plants and utilize human-made structures including houses as overwintering shelters. This article discusses the early detection and the current distribution of two invasive mosquito species, Aedes albopictus Skuse 1894 and Ae. japonicus (Theobald 1901), in Serbia, introduced in 2009 and 2018, respectively. From the first findings until today, regular monitoring has been carried out and the establishment of both species in the newly invaded areas has been confirmed. Both species can become nuisance species, especially at high population densities, but more importantly, they are capable of transmitting a wide variety of arboviruses of public health importance. This article also discusses two invasive stink bug species Halyomorpha halys Stål 1855 and Nezara viridula Linnaeus 1758, introduced in Serbia in 2015 and 2008, respectively. These two stink bug species have also been monitored, and the establishment of their populations in the country has been confirmed. Both species have caused damage to a wide range of crops and ornamental plants and sometimes become nuisance pests in urban areas.

Reproductive attributes and functional response of Anastatus japonicus on eggs of Antheraea pernyi, a factitious host

BACKGROUND

Anastatus japonicus Ashmead (Hymenoptera: Eupelmidae) is a solitary egg endoparasitoid that has been studied for inundative biological control of Halyomorpha halys Stål (Hemiptera: Pentatomidae) in China. In this study, we assessed the reproductive attributes and functional response of Anastatus japonicus on a factitious host, Antheraea pernyi (Guérin-Méneville) (Lepidoptera: Anthelidae) at 25 ± 1 °C, 70 ± 5% relative humidity and 16 h:8 h light/dark photoperiod.

RESULTS

The mean lifetime fecundity of Anastatus japonicus females was 404.3 progeny produced over an average oviposition period of 42.3 days. The sex ratio of adult progeny was slightly male biased (51.2%), whereas more female progeny were produced before day 20 of a female's life. Single 1-day-old mated Anastatus japonicus females exhibited a type II functional response to increasing host densities (1-50 eggs), with an inverse host density-dependent pattern of percent parasitism. The upper limit to the daily attack rate was estimated as 7.6 Antheraea pernyi eggs. Furthermore, mutual interference among Anastatus japonicus females occurred when increasing densities of parasitoids (1, 2, 4, 8, 16) were exposed to 30 host eggs.

CONCLUSION

Laboratory functional response result revealed that individual Anastatus japonicus might be unable to respond effectively to increasing host density in the field, which could be compensated by releasing larger numbers of wasps. Strong mutual interference among foraging Anastatus japonicus females should be considered in any future inundative biological control programs for the sustainable management of Halyomorpha halys or other host insect pests. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Attraction of Egg Parasitoids Trissolcus mitsukurii and Trissolcus japonicus to the Chemical Cues of Halyomorpha halys and Nezara viridula

Simple Summary

When an alien species reaches a new environment, the natural enemies present in that habitat might fail to regulate its population as they might not be host-adapted. Hence, the best solution might be the use of alien biological control agents that are co-evolved with the exotic pest in question. This is the case of Halyomorpha halys, which is native to Asia and has recently invaded Europe and the Americas. Trissolcus japonicus and Trissolcus mitsukurii are among its main parasitoids. Adventive populations of the latter were found in Northern Italy, suggesting its employment within augmentative biological control. Homologous programs with T. japonicus are already ongoing in Italy. This procedure implies releasing the parasitoid to increase its population and spread to new areas invaded by H. halys. However, a fundamental aspect that must be investigated is the risk-assessment beforehand, i.e., the systematic process of identifying the hazard associated with such a procedure. In this context, the preference of T. japonicus and T. mitsukurii between two stinkbugs was evaluated in this study. We found that T. japonicus preferred the naturally released traces of H. halys while T. mitsukurii exhibited a higher preference for the natural and synthetic chemical cues of N. viridula.

Abstract

Trissolcus mitsukurii and Trissolcus japonicus are two Asian egg parasitoids associated with different pentatomids such as Halyomorpha halys. Adventive populations of T. mitsukurii were found in Northern Italy, suggesting its employment as a biological control agent (BCA) against H. halys. Nevertheless, to reduce the latter’s population, T. japonicus was released in Italy. Releasing an exotic parasitoid requires investigating the interaction between the BCA and the environment to avoid negative impacts on the entomofauna of the new habitat. Trissolcus mitsukurii is mainly associated with Nezara viridula in its native area. Therefore, we investigated and compared the ability of female T. mitsukurii and T. japonicus to distinguish between naturally released cues of H. halys and N. viridula. A single parasitoid was exposed to contact kairomones of both pests to evaluate its modifications in orthokinetic and locomotory behaviour. The behaviour of female T. mitsukurii was also tested on synthetic compounds simulating the cues of the two pentatomids. When naturally released cues were used, T. japonicus preferred the traces of H. halys, while T. mitsukurii preferred N. viridula’s cues. Moreover, the attraction of T. mitsukurii to N. viridula’s cues was confirmed with synthetic cues. Additional studies are needed to judge if this parasitoid can be used as a BCA.

Olfactory responses of Trissolcus mitsukurii to plants attacked by target and non-target stink bugs suggest low risk for biological control

In crop systems, successful management of invasive insect herbivores can be achieved through the introduction of exotic biocontrol agents, parasitoids or predators, having a coevolutionary history with the pest. To avert threats to local biodiversity, recent legislations require a risk assessment for the organism to be released. Evaluation of its ability to exploit, for host location, odours associated with target and non-target species is crucial for a better definition of its ecological host range. Using Y-tube olfactometer bioassays in a quarantine laboratory, we investigated the ability of the Asian egg parasitoid Trissolcus mitsukurii (Hymenoptera: Scelionidae) to exploit odours associated with the global invader Halyomorpha halys (Hemiptera: Pentatomidae) and with non-target stink bugs native to Southern Europe. We demonstrated that T. mitsukurii is attracted by plants exposed to feeding and egg deposition of the coevolved H. halys and the native Nezara viridula, while it is not attracted by physogastric (gravid) females or eggs alone. Remarkably, T. mitsukurii is repelled by plants bearing eggs of the beneficial Arma custos. Our results contribute to a more thorough and nuanced assessment of the potential non-target risks in the case of mass-release of parasitoids as part of a biological control programme for invasive stink bugs.

New records of German Scelionidae (Hymenoptera: Platygastroidea) from the collection of the State Museum of Natural History Stuttgart

Background

Scelionid wasps are arthropod egg parasitoids, many of which are relevant to global biosecurity. However, the scelionid fauna of Germany has not received much attention from professional taxonomists.

New information

Eleven species and four genera are recorded for the first time from Germany, including species of interest to agriculture and biological control. First genus records include Baryconus Förster, Macroteleia Westwood, Paratelenomus Dodd and Probaryconus Kieffer. First species records include B.europaeus (Kieffer), Idrisnigroclavatus (Kieffer), Idrissemiflavus (Kieffer), M.bicolora Kieffer, M.pannonica Szabo, Paratelenomussaccharalis (Dodd), Trimorusvaricornis (Walker), Trissolcusbasalis (Wollaston), Trissolcusbelenus (Walker), Trissolcuscolemani (Crawford) and Trissolcusflavipes (Thompson). COI barcodes are identified for the first time from B.europaeus and M.bicolora. Each species is illustrated and updated world distributions are provided. Implications for agriculture are discussed.

First Detection of the Adventive Egg Parasitoid of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) in France

Simple Summary

The invasive brown marmorated stink bug (BMSB), Halyomorpha halys, is a polyphagous species and a serious pest worldwide. Classical biological control (CBC), i.e., the introduction of a natural enemy from the native area of the pest, is considered as the preferential solution for BMSB regulation. Adventive populations of exotic egg parasitoids of BSMB, Trissolcus japonicus and T. mitsukurii, have been reported worldwide. With the aim to characterize the French diversity of egg parasitoids associated to various stink bugs including BMSB, field surveys were conducted between 2018 and 2020. Surprisingly, morphological and molecular analyses unambiguously revealed 12 specimens of T. mitsukurii, an Asian egg parasitoid of BSMB. Although its permanent establishment has to be confirmed, this first record in France could actually facilitate CBC initiatives, T. mitsukurii being considered with T. japonicus as the two most promising biological control agents against BMSB.

Abstract

We report the first detection of Trissolcus mitsukurii in France. More than 1860 sentinel egg masses of Halyomorpha halys (BMSB) were exposed in the field during the 2018–2020 period, and 12 specimens of T. mitsukurii emerged from one egg mass. Their taxonomic identification was confirmed both by morphological and molecular analysis. Trissolcus mitsukurii, similar to T. japonicus, is an egg parasitoid of BMSB in its area of origin in Asia, and both species are considered to be candidates for a classical biological control strategy against BMSB. Trissolcus mitsukurii was previously recorded in Italy where it is well established and widespread, and this may be the source of the French population. Possible permanent establishment and dispersion of T. mitsukurii in France should be monitored with emphasis on its potential effect on BMSB populations.

Hyperparasitism of Acroclisoides sinicus (Huang and Liao) (Hymenoptera: Pteromalidae) on Two Biological Control Agents of Halyomorpha halys

Halyomorpha halys (Stål) is an invasive Asian pest that causes severe crop losses on various crops. Nowadays, management strategies against this pest mainly rely on pesticide use, but biological control with egg parasitoids is considered the most promising long-term and sustainable solution. Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) are Asian egg parasitoids already present in Europe and are the most effective biological control agents of H. halys. Therefore, these two species are considered for biological control programs in Europe and other parts of the world. Acroclisoides sinicus (Huang and Liao) is a pteromalid parasitoid wasp that frequently emerged from H. halys egg masses collected in northern Italy. This species has been hypothesized to be a hyperparasitoid of Trissolcus spp. parasitoids. This study was carried out under laboratory conditions where A. sinicus was tested in no-choice and two-choice experiments to assess the host preference between T. japonicus and T. mitsukurii. Olfactory responses of A. sinicus from volatiles emitted from different potential hosts were also tested. In all trials, A. sinicus showed a clear preference for parasitizing H. halys eggs previously parasitized by T. mitsukurii compared to T. japonicus. In no-choice experiments, the impact of the hyperparasitoid on T. japonicus was low, showing an exploitation rate of 4.0%, while up to a 96.2% exploitation rate was observed on T. mitsukurii. Acroclisoides sinicus was also attracted by volatiles emitted by egg masses parasitized by T. mitsukurii, while no response was observed to egg masses parasitized by T. japonicus or not parasitized. Therefore, according to the results obtained here, A. sinicus could limit the population development of T. mitsukurii, while lesser effects are expected on T. japonicus.

Preempting the Arrival of the Brown Marmorated Stink Bug, Halyomorpha halys: Biological Control Options for Australia

The brown marmorated stink bug Halyomorphahalys (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: Trissolcusjaponicus (Ashmead) and Trissolcusmitsukurii (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.

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 (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. 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.

Modelling the Potential Geographic Distribution of Two Trissolcus Species for the Brown Marmorated Stink Bug, Halyomorpha halys

Simple Summary

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), native to Asia, has been accidentally introduced to Europe and North America, where it has become a key pest by feeding on numerous important crops. Although H. halys has not yet established in Australia, there is a general consensus that this is only a matter of time, and thus, it is prudent to investigate management options. Previous studies have modelled the potential distribution of H. halys and one of its principal natural enemies, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae). Here, we developed a similar model of the potential distribution of Trissolcus mitsukurii (Ashmead), which is a primary parasitoid of H. halys in Japan, and which was introduced to Australia in the 1960s to control another introduced pest. We used the three models to examine the overlap in the projected distributions of both T. mitsukurii and T. japonicus with H. halys, and to assess the potential for the two Trissolcus species to help mitigate the impacts of H. halys in its global adventive range.

Abstract

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is native to northeast Asia. It was accidentally introduced to Europe and North America, where it has become a key pest, feeding on many important crops. Previous eco-climatic niche modelling indicates that H. halys could expand its distribution vastly, and numerous border interceptions of this pest in many countries, including Australia and New Zealand, indicate that it would be prudent to prepare for its eventual arrival. Similar niche modelling was used to assess the potential distribution of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), the key parasitoid of H. halys in China. Trissolcus mitsukurii (Ashmead) is one of the main parasitoids of H. halys in Japan. It is known to have existed in Australia since the early 20th century and was also specifically introduced to Australia in the 1960s, and it has now also invaded Italy. We used CLIMEX to model the climatic niche of T. mitsukurii to estimate its global potential distribution. We found that T. mitsukurii should be able to significantly expand its range globally, and that there is a significant degree of overlap in the projected ranges of T. mitsukurii, T. japonicus and H. halys. From a biological control perspective, this implies that the two Trissolcus species may be able to help mitigate the potential impacts of H. halys.

Trissolcus kozlovi in North Italy: Host Specificity and Augmentative Releases against Halyomorpha halys in Hazelnut Orchards

Simple Summary

The Asian brown marmorated stink bug, Halyomorpha halys, is an invasive crop pest introduced into Europe in the 2000s. Due to its high harmfulness, and the increased chemical use for its control in the invaded areas, research has focused on biological control. In North Italy, the native parasitoid Trissolcus kozlovi emerged from field-collected H. halys eggs and proved to successfully parasitize H. halys eggs in the laboratory. Therefore, since little is known on T. kozlovi, this study aimed at assessing its physiological host range on 12 bug species in the laboratory, as well as its potential as a biological control agent of H. halys in the field by releases in two hazelnut orchards. In the laboratory, among the tested bug species, only Nezara viridula was an unsuitable host. On all others, T. kozlovi was able to develop, even if at different levels, suggesting that it is as oligophagous as Trissolcus japonicus, with which it shares many similarities. In the field, T. kozlovi was found to parasitize H. halys eggs, but only immediately after field releases. Therefore, further field surveys are required to assess its favorably environmental conditions and its possible interaction with T. japonicus, currently present in Italy.

Abstract

Trissolcus kozlovi (Hymenoptera: Scelionidae) emerged from field-laid eggs of Halyomorpha halys (Hemiptera: Pentatomidae) in North Italy, and it emerged in significantly higher numbers from fresh H. halys eggs compared to other native scelionids. Since few data on T. kozlovi are available, its host-specificity and some biological traits were investigated in laboratory tests, and its impact after augmentative releases was evaluated in two hazelnut orchards. Among the 12 tested bug species (Hemiptera: Pentatomidae, Scutelleridae), only Nezara viridula was an unsuitable host, while the highest offspring proportions were obtained from Arma custos, Pentatoma rufipes, and Peribalus strictus, followed by Acrosternum heegeri and Palomena prasina. Furthermore, when reared on P. strictus, T. kozlovi showed a high longevity as well as a high adaptation to H. halys eggs. In both hazelnut orchards, T. kozlovi emerged from H. halys eggs after field releases, but it was not found in the next two years. The physiological host range of T. kozlovi was quite similar to that of T. japonicus, and probably T. kozlovi has just begun to attack H. halys as a new host. This aspect needs to be further investigated, as well as its favorable environmental conditions, its distribution and also its possible interaction with T. japonicus, currently present in Italy.

Assessing the Distribution of Exotic Egg Parasitoids of Halyomorpha halys in Europe with a Large-Scale Monitoring Program

Simple Summary

The management of invasive alien species is a very challenging task. For the brown marmorated stink bug (Halyomorpha halys), classical biological control has been identified as the most suitable method to sustainably reduce its populations in the long-term. Among its natural enemies, two species were identified as the most promising candidates for biocontrol, Trissolcus japonicus and Trissolcus mitsukurii. Populations of these two species have recently been detected in Europe and to assess their distribution, a large-scale study was performed. Combining several monitoring methods, in four months (May–September 2019), a wide area covering northern Italy and parts of Switzerland was surveyed. The results showed that both species have spread into all types of habitats where H. halys is present and the parasitization of native species was rarely observed. Among native species, Anastatus bifasciatus was the predominant parasitoid of H. halys. This study supported the development of the first release program of Tr. japonicus in Europe.

Abstract

The brown marmorated stink bug Halyomorpha halys is an invasive agricultural pest with a worldwide distribution. Classical biological control has been identified as the most promising method to reduce the populations of H. halys. Adventive populations of two candidates for releases, Trissolcus japonicus and Trissolcus mitsukurii, have recently been detected in Europe. To assess their distribution and abundance, a large-scale survey was performed. From May to September 2019, a wide area covering northern Italy and parts of Switzerland was surveyed, highlighting the expanding distribution of both Tr. japonicus and Tr. mitsukurii. Within four years after their first detection in Europe, both species have rapidly spread into all types of habitats where H. halys is present, showing a wide distribution and continuous expansion. Both exotic Trissolcus showed high levels of parasitism rate towards H. halys, while parasitization of non-target species was a rare event. The generalist Anastatus bifasciatus was the predominant native parasitoid of H. halys, while the emergence of native scelionids from H. halys eggs was rarely observed. The presence of the hyperparasitoid Acroclisoides sinicus was also recorded. This study provided fundamental data that supported the development of the first inoculative release program of Tr. japonicus in Europe.

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.

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.