Project : USDA ARS

ARS Home » Northeast Area » Newark, Delaware » Beneficial Insects Introduction Research Unit » Research » Research Project #429043

Research Project: Biological Control of Invasive Wood-Boring Insect Pests such as Emerald Ash Borer and Asian Longhorned Beetle

Location: Beneficial Insects Introduction Research Unit

2020 Annual Report

Objectives
Objective 1: Investigate key biotic factors influencing the spatial and temporal dynamics of wood-boring pest (including ALB and EAB) populations in their native range, focusing on exploration and quarantine service for effective, host-specific natural enemies (parasitoids) for biocontrol. Subobjective 1a - Explore for parasitoids of ALB and EAB in the pests’ native range (Asia). Subobjective 1b - Evaluate the role of the key natural enemies in regulating the spatial and temporal dynamics of ALB and EAB in the area of collection in Asia. Subobjective 1c - Evaluate the host specificity of parasitoids discovered for introduction to North America for ALB and EAB control. Subobjective 1d - Quarantine services to support research on exotic insect pests and their natural enemies. Objective 2: Conduct field releases and evaluate impacts of extant (indigenous) and previously introduced parasitoids on populations of wood-boring beetles such as EAB and ALB in the United States, while elucidating factors that influence successful establishment of introduced biological control agents, such as climate adaptation, release methodology, genetic variation in founder populations and risk-spreading (diapause) strategy. Objective 3: For newly discovered parasitoids of ALB, EAB and other invasive pests, and based on studies of life histories and reproductive biology, develop effective rearing technologies for these natural enemies, focusing on optimizing host stage, host substrate complex, temperature, photoperiod and relative humidity. Subobjective 3a - Characterize the reproductive biology, risk-spreading (diapause) strategy and key life history parameters of most promising parasitoid species. Subobjective 3b - Determine the optimal host stage and host-substrate complex in association with host density and host-to-parasitoid ratio. Subobjective 3c - Determine the optimal environmental conditions for adult parasitoid survival, oviposition and progeny development including diapause induction and termination.

Approach
Using the approaches relevant to the knowledge base of the targeted pests and their natural enemies, we will conduct foreign explorations for new natural enemies from the pests’ native home (Northeast Asia) and construct life tables of the target pest populations to evaluate the impact of the natural enemies on the pests’ population dynamics in Northeast Asia. After selecting the most promising (or efficient) natural enemies, we will test the selected natural enemies against non-target wood-boring insects in North America to delineate their host range for biological control introduction against the target pests. Upon regulatory approval for environmental releases of the discovered natural enemies in North America, we will conduct field experiments to assess their establishment, dispersal and impacts on the target pests’ population in the U.S. Laboratory studies will also be conducted to collect information on the parasitoid’s biology, risk-spreading and reproductive strategy and life history and to develop efficient rearing methods for mass-production of the introduced natural enemies for biological control releases. In addition, this project will provide quarantine services, host range data and mass-rearing technologies for natural enemies of high priority plant pests to state and federal agencies.

Progress Report
Through the support by U.S. Forest International Program (Interagency Reimbursable Agreement (IRA) 60-1926-2-043 & 60-8010-6-004 and collaborations with Chinese Academy of Forestry (Non-Assistance Cooperative Agreement (NACA) 58-8010-5-001F & 58-8010-7-005F), we collected and described three new species of encyrtid parasitoids of the emerald ash borer from Northeast Asia (the Russian Far East and China) during the life cycle of the project (Objective 1). One of the new egg parasitoids, O. primorskyensis, has been imported to the Newark USDA quarantine facility, tested for host specificity and is now being evaluated for environmental releases against emerald ash borer in the U.S. Working with cooperators from China, South Korea, and Animal and Plant Health Inspection Service (APHIS), we surveyed Asian longhorned beetle parasitoid guilds and their seasonal abundance using field-deployed sentinel host eggs or larvae in China (Beijing City, Shanghai City, and Jilin Province) and South Korea. Our survey in China detected over 12 species of hymenopteran parasitoids (four Pteromalidae, three Braconidae, two Eupelmidae, one Eurytomidae, one Ichneumonidae, and one Bethylidae) attacking sentinel Asian longhorned beetle larvae or eggs deployed in these sites (Li et al. 2020). Among all the parasitoid species recovered, the four most abundant species have been imported to the Beneficial Insects Introduction Research Unit (BIIRU) quarantine for further evaluation of their reproductive biology and host specificity. In South Korea, at least one egg parasitoid and one larval parasitoid were collected, but they have not been identified to species yet. In addition, over 120 permitted consignments were received annually by the Quarantine Facility from 2015 to 2020, consisting of over 10,000 specimens and 20 different beneficial species. A total of 53 outgoing shipments (~700 pest specimens; 150,000 parasitoids in 8 genera) were shipped to different cooperators in four states plus Canada every year. A total of 57 identification requests were submitted to the ARS Systematic Entomology Laboratory for determination. From 2015 to 2020, a total of 15 collaborators from 10 different states and Canada were involved in quarantine services. Through collaborations with the University of Massachusetts (NACA 58-5010-5-013), University of Maryland (58-8010-5-015), Virginia Tech (58-8010-5-016), USDA APHIS (IRA 60-8010-9-001), and U.S. Forest Service, we conducted field releases and evaluations of three previously introduced Chinese parasitoids as well as a more recently introduced Russian larval parasitoid in Michigan, Maryland, and Northeastern U.S. (Massachusetts, New York, Connecticut) and Virginia (Objective 2). Based on data collected from our study sites in these States, we constructed life tables of the emerald ash borer populations and quantified the role of both the native North American natural enemies and introduced biocontrol agents in suppressing the pest’s population growth rate. Using quantitative life-table analysis, we discovered that native North American natural enemies (a parasitoid wasp and woodpeckers) play a key role in suppressing the outbreak population of the invading emerald ash borer in central Michigan, but one introduced biocontrol agent became the dominant mortality factor of emerald ash borer larvae in small ash trees and ash saplings in the aftermath of emerald ash borer invasion (approximately five years after its releases there). However, the role of that agent in protection of large ash trees will be limited or inactive because of its short ovipositor (1.5 - 2.5 mm). Our recent field study showed that the more recently introduced parasitoid with a much longer ovipositor (4 – 5 mm) caused nearly 50% beetle mortality (by parasitism) approximately 2 years after major releases in some of our study sites in Northeastern U.S. It is expected that this newly introduced larval parasitoid and an Asian egg parasitoid may provide effective protection of large ash trees against emerald ash borer. Findings from these field studies also showed that the most recently introduced Russian larval parasitoid along with the earlier introduced agent have established increasing populations and spread widely in our study sites in Michigan, Massachusetts, New York, and Connecticut, where it was released between 2015 – 2017 (Duan et al. 2019). However, findings from the study in Michigan also showed that approximately 18–50% of parasitoid larvae were killed by extreme winter weather due to the 2019 polar vortex (Duan et al. 2020), indicating that extreme climates may negatively affect the efficacy of emerald ash borer biocontrol. In addition, our field study in Maryland and Virginia also suggests that the diapause status and release time affect the synchronization of the parasitoids and beetle populations and thus their establishment in the released regions (Abel et al, 2019; George et al. 2020, Ragzzino et al. 2020). For our field work testing the augmentative releases of a North American parasitoid against the invasive Asian Longhorned beetle population in the quarantined area (Worcester, Massachusetts), we have recently gathered and submitted the necessary safety data to USDA APHIS and Massachusetts State Conservation Department for their review and approval of the work permit in Worcester, Massachusetts. Significant progress has been made in developing effective rearing technologies for emerald ash borer and Asian longhorned beetle natural enemies used for biological control of the target pests (Objective 3). This includes the successful development of an evergreen ash-based rearing system for year-around production of various life stages of emerald ash borer for parasitoid production. Using this host-rearing method, we have successfully determined the key life-history parameters and optimal rearing conditions (temperature, host stage, host-to-parasitoid ratio and group structures) for the previously introduced emerald ash borer parasitoids. In addition, we have recently evaluated the potential of a native North American parasitoid as a novel association control agent for Asian longhorned beetle, by charactering various aspects of the parasitoid’s reproductive traits, including egg maturation dynamics, host size preference and suitability in association with Asian longhorned beetle. Our results showed that female wasps emerged with a substantial portion of their lifetime complement of mature eggs. Mature egg load reached a peak 4–6 d post-eclosion, and mature egg load also increased with female’s body size. Oviposition prompted production of more mature eggs in young female wasps. The parasitoid did not show a significant preference for large over small hosts in a choice test. Offspring survival, developmental time and sex ratio were not affected by host size. However, clutch size increased with host size and female wasps that developed from the large host had a larger body and consequently higher mature egg load than those reared from the small host. Neither longevity nor total number of parasitized hosts over a female lifetime were affected by female’s body size, but life-time fecundity, in terms of total number of offspring produced, increased with the female’s size. These results have important implications for improving rearing and field-release protocols of this parasitoid and have been submitted for publication (Log No: 373071). To further optimize the conditions for mass-rearing the native parasitoid for augmentative field releases, we have Investigated effects of different densities of host and parasitoid on its parasitization efficiency and reproductive outcomes. Results showed that overall parasitism and total numbers of parasitized hosts or progeny produced increased with host and/or parasitoid densities, but the number of parasitized hosts or progeny produced per female parasitoid decreased with parasitoid density at each given host density. Female parasitoids responded to increased parasitoid density with a significant increase in clutch size. Overall, per capita parasitization efficiency or reproductive outcomes were optimized at a low parasitoid-host ratio but with large group size of hosts and parasitoids. An optimal combination of exposing three or four parasitoids to four hosts is proposed for efficient mass-rearing of this parasitoid (Log No: 374591).

Accomplishments
1. Biocontrol for emerald ash borer to protect North American ash trees. The emerald ash borer is a serious invasive forest pest that has destroyed natural and urban ash forests and threatens the existence of North American ash species. ARS researchers at Newark, Delaware, introduced a parasitic wasp, Spathius galinae, which has established a self-sustaining population three years after its release. The wasp has now spread to other infested areas and is providing significant biocontrol of the borer in large ash trees in the northeast United States. This natural enemy of emerald ash borers is critical for the protection of large ash trees in the U.S. forest ecosystems.

2. A new parasite that attacks the Asian longhorned beetle discovered. The Asian longhorned beetle is a high-risk, invasive forest pest that has established small populations in several U.S. states and threatens to cause severe damage to American hardwood forests if not successfully controlled or eradicated. ARS scientists at Newark, Delaware, working with researchers at USDA Animal Plant Health and Inspection Service and collaborators in China recently discovered and collected several new wasp parasites from northern China and brought them to Newark for evaluation of their host specificity.

U.S. DEPARTMENT OF AGRICULTURE

Beneficial Insects Introduction Research Unit: Newark, DE