1a. Objectives (from AD-416):
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.
1b. Approach (from AD-416):
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.
3. Progress Report:
No additional progress was made in foreign exploration for emerald ash borer (EAB) natural enemies in northeast China, Korea and the Russian Far East for this fiscal year (objective 1a). With the support from U.S. Forest Service International Program and collaboration with Chinese scientists at the Chinese Academy of Forestry, we made substantial progress in evaluating the role of key natural enemies in regulating population dynamics of emerald ash borers and Asian longhorned beetles in their native range (Objective 1b). In addition, most 36-milestones for Objectives 2 and 3 of the emerald ash borer project were substantially met for this fiscal year. Detailed progress for fiscal year 2018 in accomplishing objectives of both emerald ash borer and Asian longhorned beetle research is described below: EMERALD ASH BORER RESEARCH: With support from the U.S. Forest Service International Program and cooperators at the Chinese Academy of Forestry (Objective 1b), a total of 30 ash trees were sampled in the spring of 2018 (April 15 – 29) from three different study sites located in central and southwest China. The sampled ash trees had been artificially infested in the previous (2017) summer with emerald ash borer eggs, including the North American species (Fraxinus velutina) central China (Xucheng city in Henan Province), the Chinese ash species - Fraxinus griffithii in south China (Guilin, Guanxi Province) and F. chinensis in southwest China (Leshan city, Sichuan province). In addition, Lindgren multi-tunnel traps were also deployed at each study site (4 traps per sites) to capture emerald ash borer adults (if they occur at the study sites). Results of our 2018 China study showed that the dominant (perhaps only) ash trees in south or southwest China, are oriental ash species - F. griffithii in Guanxi province and F. chinensis in Sichuan province. These native Chinese ash trees appear to be highly resistant to emerald ash borer larvae. All artificially established emerald ash borer cohorts (N ~ 150) were killed at early instars (1 – 3rd) in these two locations. No adult EAB were captured in the Lindgren traps, nor were wild EAB larvae observed from the ash trees that were previously girdled. Together, these findings indicate that Chinese native host tree resistance may be a key factor to prevent EAB establishment in south and/or southwest China. In central parts of China, however, the North American ash (F. velutina) is widely planted. While no wild EAB larvae were observed in our sampling trees, nor were any adults captured in the Lindgren funnel traps, we found that artificially established EAB cohorts on North American ash (F. velutina) trees successfully developed to adult stages in central China. We observed 100% parasitism by a braconid parasitoid of the artificially established EAB larvae from one of the six infested trees. The adult parasitoids had already exited from the cocoons and could not be collected and identified to species. Based on the characteristic of the cocoon, it was identified as Atanycolus sp. Further work is planned to collect this parasitoid from this location. Results of our field studies in 2018 in Central China raise questions as to why EAB doesn’t occur in this part of China, where susceptible host plants (F. velutina) appear to be abundant in plantations and urban landscapes and climatic conditions are suitable for EAB larval development to adults. It is possible that natural enemies may have played a key role in preventing EAB from spreading to this part of China or more time is needed for EAB to naturally spread from nearby known EAB-infested regions such as Hebei and Shandong provinces. Considering the current spread of the EAB in the U.S. to the southern states such as Tennessee, Georgia and Louisiana, it is important to investigate the factors that may have limited the EAB spread to further central and southern parts of China - i.e., no known EAB distribution in the south to Hebei Province (including Tianjin and Beijing). For Objective 1c, we completed the host specificity testing of the newly described emerald ash borer egg parasitoid, Oobius primorskyensis, from the Russian Far East against 30 species of nontarget insects, including mostly native North American wood-boring beetles in the families Buprestidae and Cerambycidae plus one unidentified weevil, one predatory coccinellid, one pentatomid and one moth. Results from our host specificity testing showed that O. primorskyensis attacked seven out of nine non-target Agrilus species, but not any of the other non-target species tested. Percentage parasitism of some non-target Agrilus species (A. anxius and A. cephalicus was comparable to parasitism of their corresponding EAB control at 29 - 30%). However, percentage parasitism of most attacked non-target Agrilus species (A. bilineatus, A. egenus, A. fallax, A. macer, and A. oblongus) was significantly less (4 – 17%) than for the EAB control (60 – 90%). These results indicate that the host specificity of O. primorskyensis may be limited to species in the genus Agrilus, especially those most phylogenetically related to EAB, although additional testing is needed to determine whether the eggs of other buprestid genera are utilized by the species as well. In cooperation with the university and state cooperators, we continued to monitor the establishment and impact of previously introduced EAB parasitoids (Oobius agrili, Tetrastichus planipennisi, Spathius agrili and S. galinae) on EAB densities in Maryland, Virginia, Michigan, Massachusetts, New York and Connecticut (Objective 2). All four biocontrol agents have been recovered following their releases in most release sites in these States; however, only T. planipennisi and O. agrili have been consistently recovered more than one year following their releases. Our 2018 data indicates that the introduced biocontrol agent T. planipennisi continues to provide significant biocontrol services in the earliest release sites in southern Michigan, where releases of T. planipennis were conducted between 2007 – 2010. In addition, working with collaborators from University of Maryland, University of Delaware, and U.S. Forest Services, we determined the optimal temperature/photoperiod regimes for induction and termination of emerald ash borer parasitoid O. agrili and Tetrastichus planipennisi and thus improved the current rearing protocols for these parasitoids (Objective 3c). ASIAN LONGHORNED BEETLE RESEARCH: Working with the Cooperator at the Chinese Academy of Forestry, we analyzed field-survey data collected from four Chinese provinces between 2015 and 2017 on mortality factors affecting eggs, immatures (larvae and pupae combined), and adults of the Asian longhorned beetle (ALB) infesting willows and poplar trees (Objective 1b). Our analyses showed that immature ALB density varied by location and tree species; however, overall density was highest in Jilin province. When immature ALB density was compared between host tree species from the same province, nearly four times the immature numbers were found infesting poplar than willow trees. On average, 59.3% of ALB eggs were killed by undetermined factors (likely host tree resistance and microbial pathogens) across all survey sites and years. In contrast, immature ALB stages were least susceptible to mortality factors, where on average 8.3%, 15.6%, and 9.1% of these were killed, respectively, by undetermined factors, woodpeckers, and unidentified predators across all survey sites and years. Parasitoids, Dastarcus helophoroides and Sclerodermus guani, were recovered from immatures in Gansu and Shaanxi provinces and Beijing City, together accounting for around 6.0% mortality of these stages in these sites. Working with cooperators from the USDA-APHIS Otis laboratory, we initiated host specificity testing of D. helophorides against nontarget wood-boring beetles (Objective 1c). Preliminary findings from our host specificity testing indicate that many native North American cerambycids and buprestids would be vulnerable to D. helophoroides and we thus recommend that D. helophoroides should not be considered for release as a biocontrol agent in North America. QUARANTINE SERVICE: We provided essential quarantine services for two other ARS research projects at the Beneficial Insects Introduction Research Unit as well as several ARS cooperators (Objective 1d). These activities included receipts of a total of 104 permitted consignments, consisting of 4652 pest specimens, and 2825 parasitoids, and sending 31 outgoing shipments with 1900 pest specimens, and 2590 parasitoids. In addition, we successfully maintained daily quarantine operation and updated quarantine facility and cultured 18 species of living insect colonies.
1. Two natural enemies of Emerald Ash Borers discovered. Exotic wood-boring insects such as emerald ash borer (EAB) can become serious invasive tree pests when accidentally introduced to new regions or areas. Discovery of new natural enemies in the pests’ native range can greatly enhance the potential for biological control of these invasive or potentially invasive pests in the U.S. Scientists from the Chinese Academy of Forestry, USDA-ARS and U.S. Forest Service discovered and subsequently described two new species of parasitoids collected from the eggs of a wood-boring beetle (Agrilus fleischeri) infesting poplar trees in northeastern China where EAB also occurs. These new species (Oobius saimaensis and O. fleischeri) also attack EAB eggs in the laboratory and are additional agents for potential introduction to the U.S. for biological control of EAB.
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Yao, Y., Duan, J.J., Mottern, J.L., Wang, X., Yang, Z., Bauer, L.S. 2018. Two new species of Oobius Trjapitzin (Hymenoptera: Encyrtidae) and their phylogenetic relationship with other congeners from Northeastern Asia. The Canadian Entomologist. 150:303-316. https://doi.org/10.4039/tce.2018.17.
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Rodrigues, T.B., Duan, J.J., Rieske, L.K., Palli, S.R. 2018. Identification of highly effective target genes for RNAi-mediated control of emerald ash borer, Agrilus planipennis. Scientific Reports. 8:5020. http://doi.org/10.1038/S41598-018-23216-6.
Kashian, D.M., Bauer, L.S., Spei, B.A., Duan, J.J., Gould, J.R. 2018. Potential impacts of emerald ash borer biocontrol on ash health and recovery in southern Michigan. Forests. 9(6):296. https://doi.org/10.3390/f9060296.