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.
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.
No additional progress was made in quantifying recruitment of ALB and EAB stages and associated parasitoids in the pests’ native range (Objective 1a – 48 months milestones) for this fiscal year. With the support from United States Forest Service International Program and USDA APHIS, additional work has been planned this summer through next fiscal year to continue the quantification of impacts of Asiatic natural enemies on the Asian longhorned beetle (ALB) and emerald ash borer (EAB) populations via life-table recruitment studies in South Korea and China, respectively. In addition, we have not been able to select appropriate sites for releasing the North American native parasitoid (Ontsira mellipes) due to low ALB densities in quarantined areas and also permit requirement for deploying sentinel ALB larval logs (Objective 2 – 48 months milestones). Other than the above not-met milestones, the rest 48 months milestones for Objectives 1, 2 and 3 of both the ALB and the EAB projects were fully or substantially met for this fiscal year. Detailed progress for fiscal year 2019 in accomplishing objectives of both ALB and EAB research is described below: ASIAN LONGHORNED BEETLE RESEARCH: Working with cooperators from the USDA APHIS Otis laboratory, we tested the host specificity of the native North American larval parasitoid (O. mellipes) against two invasive longhorned beetles [ALB Anoplophora glabripennis; Citrus longhorned beetle (CLB)– A. chinensis] and six common North American cerambycid species (Elaphidion mucronatum, Monochamus carolinensis, Monochamus notatus, Neoclytus scutellaris, Xylotrechus colonus, and Xylotrechus sagittatus) (Objective 1C). Results of our host specificity testing showed that the native North American parasitoid (O. mellipes) readily attacked ALB, CLB, and three north American longhorned beetle species (E. mucronatum, M. carolinensis and M. notatus), but did not attack the other three north American longhorned beetle species (Wang et al. 2019, submitted). In addition, our study showed that O. mellipes performed equally well on ALB as on its native North American hosts such as M. carolinensis, indicating that the effect of O. mellipes on ALB could be enhanced in the presence of these alternative and native hosts to support local parasitoid populations in the field. More interestingly, we have found that the performance of O. mellipes on ALB can be significantly improved through continuous rearing on ALB in the laboratory (Golec et al. 2019). To optimize the condition for mass-rearing O. mellipes for augmentative field releases, we investigated some key reproductive traits of the parasitoid, including egg maturation dynamics, host size preference and suitability, as well optimal host to parasitoid ratio in terms of parasitism or offspring production per female. Results showed that female O. mellipes emerged with ca. 15 mature eggs and mature egg load peaked after 4–6 days to ~40 mature eggs. Number of mature eggs was also positively related to the female’s body size. Female parasitoid preferred to attack middle sized hosts (400-600 mg) and brood size positively increased with host body mass within the host size range (20-800 mg). Above this range brood size no longer increased with the host size. The parasitoid was able to estimate host size most likely based on the host’s defense capacity as the clutch size was also positively related to the number of stings (i.e. stinging and releasing venom to paralyze the host prior to oviposition). We tested a range of different ratios of wasps to hosts (1 to 15 wasps and 2 to 4 hosts, n = 1660). These findings suggest the parasitoid is likely most active when it is 4-6 days old, and more productive when using middle sized hosts and a ratio of approximately 3 wasps to 1 host. EMERALD ASH BORER RESEARCH: Considering the current spread of the EAB in the United States 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 its native range China - i.e., no known EAB distribution in the south to Hebei Province (Objective 1b – 48 milestones). With the financial support by the U.S. Forest Service International Program and cooperators from Chinese Academy of Forestry, we continued our exploration for natural enemies in central and south China by deploying EAB-infested ash logs in the expanded area of central and southwest China, including Changsha in Hunan Province, Xinyang and Xucheng in Henan province, Leshan in Sichuan province, and Fuchou in Fujian province, where no emerald ash borer infestations had been observed. The sentinel ash logs (each about 50 cm long x 12.cm in diameter) were created with artificially infested EAB eggs (15 eggs per log) in July of 2018 and deployed to each of the study sites (10 logs per site) approximately two weeks after the egg infestation. These sentinel logs were then sampled in April of 2019 for EAB parasitoids. We hypothesized that these sentinel emerald ash borer larval logs would attract natural enemies such as parasitoids of wood-boring insects in these native regions, where densities of naturally occurring emerald ash borers (if any) would be too low to allow any detection. Unfortunately, few emerald ash borer larvae infesting the sentinel ash logs survived beyond 3rd instars and no natural enemies (larval parasitoids) were detected in any of these field-deployed logs. Upon dissection, we found that the nearly complete mortality of the EAB larvae inside the sentinel ash logs was due to the desiccation of the cambium tissues of the sentinel ash logs as no evidence of parasitism was observed. We discussed these results with our Chinese cooperators and suggested using girdled-trees (instead of sentinel logs) for future studies (if funds are available). For Objective 1c (48 months milestones), we completed all the physical work on the host specificity testing of the newly described emerald ash borer egg parasitoid, Oobius primorskyensis in the previous fiscal year and published the results of the study in this fiscal year (Duan et al. 2018). Our findings strongly indicate that the host specificity of O. primorskyensis is limited to species in the genus Agrilus, especially those most phylogenetically related to EAB. Results of this study will be used in the future petition for regulatory approval of this newly discovered egg parasitoid for environmental releases against EAB in North America. With university and state cooperators, we continued to collect data on population densities of EAB eggs and larvae and associated natural enemies in our biological control release sites in Maryland, Virginia, Michigan, Massachusetts, New York and Connecticut (Objective 2 – 48 milestones) in this fiscal year. The impact of both introduced and North America native natural enemies on the invasive emerald ash borer populations was quantified with life table analysis constructed from these data as well as data collected previously. Findings from the life table analysis showed that the most recently introduced larval parasitoid (Spathius galinae) has established increasing populations in all the release sites in Michigan (6), Massachusetts (2), New York (2) and Connecticut (3), where it was released between 2015 – 2017 and its density had increased 1.5 to 20-fold (relative to the first post-release sample year), reaching a final density of 2.3 – 14.3 broods/m2 of phloem area and causing 13.1 – 49.2% marginal rate of parasitism at some of the release sites (Duan et al. in press). It’s hopeful that this newly introduced larval parasitoid (S. galinae), along with earlier introduced agents (T. planipennisi and O. agrili) will provide a whole spectrum of protection of North American ash against EAB (Jennings et al. 2018, 2019). For fiscal year 2019, we continued to optimize the rearing and storage (temperature) conditions for the newly described egg parasitoid O. primorskyensis as well as the previously introduced egg parasitoid O. agrili (Objective 3c- 48 milestones). We exposed diapausing O. primorskyensis and O. agrili larvae to either 1.7°C or 12.8°C for 1 – 9 months, subsequently evaluated their post-chill development to adults, and assessed the longevity and lifetime fecundity of the emerged adult parasitoids under normal rearing conditions (25°C, 16:8 h L:D). Results of this show that both parasitoid species require periods of chill at either 1.7°C or 12.8°C to resume their development to adults under normal rearing conditions; however, there are clear differences between the two species in their responses to chill regimes. These findings have relevance to laboratory rearing and release strategies of these parasitoids for biocontrol of EAB and have been recently published in a peer reviewed journal (Duan and Larson 2019). 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 – 48-month milestones). These activities included receipts of a total of 61 permitted consignments of three targeted pests and five species of natural enemies, consisting of incoming shipments of 2472 EAB beetles and 2549 EAB larval and egg parasitoids (219 Spathius agrili, 1530 Spathius galinae, 400 Tetrastichus planipennisi and 800 Oobius agrili), 4 different chalcid parasitoids, 3 separate braconid parasitoids, as well as hand carried shipments of 150 spotted lanternfly (Lycorma delicatula). In addition, we had 5 outgoing shipments of 1440 EAB larval parasitoids (Spathius galinae) and 6 shipments of ALB eggs totaling 600 to support cooperator’s research programs at the University of Massachusetts and University of Kentucky, respectively.
Duan, J.J., Schmude, J.M., Larson, K.M., Fuester, R.W., Gould, J.R., Ulyshen, M. 2018. Field parasitism and host specificity of Oobius primorskyensis (Hymenoptera: Encyrtidae), an egg parasitoid of the emerald ash borer (Coleoptera: Buprestidae) in the Russian Far East. Biological Control. 130: 44-50. https://doi.org/10.1016/j.biocontrol.2018.12.005.
Wang, X., Hogg, B.N., Hougardy, E., Nance, A., Daane, K.M. 2018. Potential competitive outcomes among three solitary larval endoparasitoids as candidate agents for classical biological control of Drosophila suzukii. Biological Control. 130:18-26. https://doi.org/10.1016/j.biocontrol.2018.12.003.
Jennings, D.E., Duan, J.J., Shrewsbury, P.M. 2018. Comparing recovery methods for the emerald ash borer (Agrilus planipennis, Coleoptera: Buprestidae) egg parasitoid Oobius agrili (Hymenoptera: Encyrtidae) in Maryland, USA. Forests. 659(9): 1-9. https://doi.org/10.3390/f9100659.
Jennings, D.E., Xiao-Yi, W., Duan, J.J. 0219. Influence of density on interspecific competition between Spathius galinae and Tetrastichus planipennisi, larval parasitoids of the invasive emerald ash borer (Agrilus planipennis). Environmental Entomology. 48(2), 2019, 404–409. https://doi.org/10.1093/ee/nvz008.
Golec, J., Duan, J.J., Rim, K.A., Aparicio, E.M., Hough-Goldstein, J. 2019. Laboratory adaptation of a native North American parasitoid to a novel, invasive insect pest. Ecology and Evolution. 92:1179–1186. https://doi.org/10.1007/s10340-019-01101-z.
Duan, J.J., Larson, K. 2019. Effects of chilling on diapause development and reproductive fitness of two congeneric species of encyrtid parasitoids (Hymenoptera: Encyrtidae) attacking the invasive emerald ash borer. Biological Control. 134: 163-169. https://doi.org/10.1016/j.biocontrol.2019.04.010.
Lee, J.C., Wang, X., Daane, K.M., Hoelmer, K.A., Isaacs, R., Sial, A., Walton, V. 2019. Biological control of spotted-wing drosophila (Diptera: Drosophilidae) - Current and pending tactics. Journal of Integrated Pest Management. 10(1):1-9. https://doi.org/10.1093/jipm/pmz012.