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

Reproductive biology of overwintering leaffooted bug Leptoglossus zonatus (Hemiptera: Coreidae) in California

Leptoglossus zonatus (Dallas) (Hemiptera: Coreidae) is a polyphagous insect pest attacking a wide variety of crops. In California's Central Valley, it is now the dominant leaffooted bug on almonds, pistachios, and pomegranates. Leptoglossus zonatus pest status depends largely on overwintering adult survival and reproductive potential, which determines its population size in spring and early summer when nut crops are particularly susceptible to bug damage. Here, we investigated the overwintering reproductive biology of L. zonatus in laboratory and field experiments to gain information about its ovary development, time of mating, and the impact of low temperatures on egg hatch. With dissections of laboratory-reared L. zonatus, we established a baseline for ovarian development and determined that the size of the spermathecal reservoir is larger in mated than in unmated females. Dissections and behavioral experiments of field-collected material provided evidence of mating events before dispersal from overwintering sites. Laboratory trials showed that temperature significantly impacted L. zonatus egg hatch. Leptoglossus zonatus reproductive biology presented provides valuable information on its population dynamics and dispersal from overwintering sites, and will contribute to the development of monitoring and management tools.

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.

Partial refuges from biological control due to intraspecific variation in protective host traits

Predicting how much of a host or prey population may be attacked by their natural enemies is fundamental to several subfields of applied ecology, particularly biological control of pest organisms. Hosts or prey can occupy refuges that prevent them from being killed by natural enemies, but habitat or ecological refuges are challenging or impossible to predict in a laboratory setting-which is often where efficacy and specificity testing of candidate biological control agents is done. Here we explore how intraspecific variation in continuous traits of individuals or groups that confer some protection from natural enemy attack-even after the natural enemy has encountered the prey-could provide partial refuges. The size of these trait-based refuges (i.e., the proportion of prey that survive natural enemy encounters due to protective traits) should depend on the relationship between trait values and host/prey susceptibility to natural enemy attack and on how common different trait values are within a host/prey population. These can be readily estimated in laboratory testing of natural enemy impact on target or nontarget prey or hosts as long as sufficient host material is available. We provide a general framework for how intraspecific variation in protective host traits could be integrated into biological control research, specifically with reference to nontarget testing as part of classical biological control programs. As a case study, we exposed different host clutch sizes of target (pest) and nontarget (native species) stink bug (Hemiptera: Pentatomidae) species to a well-studied exotic biocontrol agent, the egg parasitoid Trissolcus japonicus (Hymenoptera: Scelionidae). We predicted that the smallest and largest clutches would occupy trait-based refuges from parasitism. Although we observed several behavioral and reproductive responses to variation in host egg mass size by T. japonicus, they did not translate to increases in host survival large enough to change the conclusions of nontarget testing. We encourage researchers to investigate intraspecific variation in a wider variety of protective host and prey traits and their consequences for refuge size.

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.

Effects of different Philosamia ricini (Lepidoptera: Saturniidae) cold storage periods on Ooencyrtus pityocampae and Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) rearing

Ooencyrtus pityocampae and Ooencyrtus kuvanae are egg parasitoids that are considered potential candidates for the control of different pest species through inundative release. The aim of this study was to assess the effects of different cold-storage periods of Philosamia ricini eggs (host) on the rearing parameters of O. pityocampae and O. kuvanae. Host eggs were stored at 3 °C, and a factorial experiment involving two parasitoid species, nine host storage periods (1, 5, 10, 15, 30, 45, 60, 75 and 90 days) and a control, and two host ages (1 and 2 days) was conducted, with 10 replications including 40-P. ricini eggs each. Adult emergence, development time, longevity, and fecundity were investigated. The parasitoid adult emergence percentage significantly varied with storage duration. These values were lower in O. kuvanae than in O. pityocampae. The development time of O. kuvanae progeny increased in both host age groups except in the 1-day storage period subgroup. However, the development times of the progeny of O. pityocampae reared on one-day-old eggs stored for 5, 10, 60, and 75 days were increased, and the development times of the progeny of O. pityocampae reared on 2-day-old eggs stored for 45 and 90 days were increased. The longevity of the F1 progeny of O. kuvanae was negatively affected by storage time. There was no difference in the longevity of the F1 progeny of O. pityocampae compared to that of the control. Additionally, the fecundities of the F1 progeny of O. pityocampae and O. kuvanae were 54.7 and 47.0 offspring/female, respectively. These results provide useful information for guiding the development of mass rearing methodologies for both parasitoid species.

Implementing Mass Rearing of Trissolcus japonicus (Hymenoptera: Scelionidae) on Cold-Stored Host Eggs

Simple Summary

Halyomorpha halys (Stål) (Heteroptera: Pentatomidae) is a polyphagous and invasive pest that has been causing severe damage to agricultural systems worldwide including Italy. Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), an egg parasitoid native to regions of Asia where H. halys originated, seems to be one of the most promising solutions for decreasing pest pressure. In 2020, field releases of T. japonicus were approved in Italy with the aim of releasing 120,000 parasitoids. Thus, it was necessary to develop an efficient rearing system to support this biological control program. In this study, some parameters that could influence the rearing of T. japonicus on cold-stored eggs of H. halys were investigated. Refrigeration at 6 °C for as long as several months is an effective method of storage for H. halys egg masses. Female parasitoids produced the highest number of progeny when exposed to egg masses for 72 h. Adult wasps could also be stored at 16 °C for up to 90 days with a negligible decrease in survival, but a significant decrease in production of progeny.

Abstract

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), a pest of Asian origin, has been causing severe damage to Italian agriculture. The application of classical biological control by the release of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), an exotic egg parasitoid, appears to be one promising solution. In Italy, releases of T. japonicus in the field were authorized in 2020. In this study, some parameters that could influence the rearing of T. japonicus in insectaries were investigated. A significantly higher production of progeny was observed on host eggs stored at 6 °C (86.5%) compared to −24 °C (48.8%) for up to two months prior to exposure to parasitism. There were no significant differences in progeny production from single females in a vial provided with only one egg mass (83.2%) or 10 females inside a cage with 6 egg masses (83.9%). The exposure of parasitoids to refrigerated (6 °C) egg masses of H. halys for 72 h led to a significantly higher production of progeny (62.1%) compared to shorter exposures for 48 (44.0%) or 24 h (37.1%). A decline in production of progeny by the same female was detected between the first (62.1%) and the second parasitization (41.3%). Adult parasitoids stored at 16 °C for up to 90 days had an 87.1% survival rate, but a significant decrease in progeny production was detected. These parameters could be adjusted when rearing T. japonicus for specific aims such as the production of individuals for field release or colony maintenance.

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.