New associations between parasitoid species is common in biological control with interactions ranging from coexistence to competitive exclusion. Spathius agrili and Spathius galinae, native to North East Asia, are two host-specific idiobiont larval parasitoids of the invasive emerald ash borer Agrilus planipennis that do not overlap in their native ranges but have been recently introduced to the United States for biocontrol of A. planipennis. We conducted laboratory experiments to determine the results of competition between these two species. Competition between parasitoid larvae on a single host (intrinsic competition) and competition between adult parasitoids for oviposition sites (extrinsic competition) were evaluated. Successful multiparasitism did not occur in any intrinsic trials. Extrinsic competition favored S. agrili, but S. galinae was not excluded. Competition lowered parasitism rates for both species, but overall parasitism was not lowered. ; USFS Grant [15-DG-11083150-042]; USDA ARS Grant [58-8010-5-016] ; Published version ; This research was funded through USFS Grant 15-DG-11083150-042 and USDA ARS Grant 58-8010-5-016. ; Public domain authored by a U.S. government employee
Both Spathius agrili Yang and Spathius galinae Belokobylskij and Strazanac are host-specific parasitic wasps introduced for biological control of emerald ash borer in North America. Spathius agrili is native to northeastern China and S. galinae comes from a more northern, colder climate in the Russian Far East. Their origin may lead to differing abilities to adapt to climate and their host in North America. We conducted both field and laboratory experiments to determine the timing of early season emergence and synchronization of each parasitoid species to their host in the United States, and if manipulating prerelease conditions could affect emergence time. A cold acclimatization treatment prior to parasitoid emergence was assessed and compared with untreated control group reared with standard rearing protocols. Stands of naturally emerald ash borer-infested ash were sampled at two locations in Virginia throughout the experiment to determine when the parasitoid-susceptible life stage (third to fourth instar) occurred. Untreated S. galinae emerged approximately 2 wk earlier than any other cohort, whereas cold acclimatized S. galinae emerged later than any other cohort. Emergence time of S. agrili was unaffected by cold acclimatization. Cold acclimatization treatment did not affect the parasitism rate of either species, nor did it have multigenerational effects. Emergence time of the subsequent generation of S. agrili was delayed by cold acclimatization treatment, whereas S. galinae experienced no multigenerational effects. At Virginia field sites, susceptible EAB larvae were present during the emergence time of all four groups of parasitoids. Untreated S. galinae had the least overlap with any susceptible EAB larvae. ; U.S. Forest Service Cooperative Forest Health Grant [15-DG-11083150-042]; USDA ARS Grant [58-8010-5-016] ; We would like to thank Brandi Benedict, Fitz Cherry, and Rachel Campbell for the hours of bolt dissections, emergence counting, and colony maintenance. Thank you to Kristi Larson, the BIIRU lab, and the APHIS Brighton Facility for rearing the insects for these experiments. Additional thanks to Erin Langton-Ragozzino, Miranda Pacheco, and Liam Sullivan for graciously helping review an early draft of this manuscript. This was funded through a U.S. Forest Service Cooperative Forest Health Grant 15-DG-11083150-042 and USDA ARS Grant 58-8010-5-016. ; Public domain authored by a U.S. government employee
The hemlock woolly adelgid, Adelges tsugae Annand is an invasive insect that frequently causes hemlock (Tsuga spp.) mortality in the eastern United States. Studies have shown that once healthy hemlocks become infested by the adelgid, nutrients are depleted from the tree, leading to both tree decline and a reduction of the adelgid population. Since A. tsugae is dependent on hemlock for nutrients, feeding on trees in poor health may affect the ability of the insect to obtain necessary nutrients and may consequently affect their physiological and population health. Trees were categorized as lightly or moderately impacted by A. tsugae based on quantitative and qualitative tree health measurements. Population health of A. tsugae on each tree was determined by measuring insect density and peak mean fecundity; A. tsugae physiological health was determined by measuring insect biomass, total carbon, carbohydrate, total nitrogen, and amino nitrogen levels. Adelges tsugae from moderately impacted trees exhibited significantly greater fecundity than from lightly impacted trees. However, A. tsugae from lightly impacted hemlocks contained significantly greater levels of carbohydrates, total nitrogen, and amino nitrogen. While the results of the physiological analysis generally support our hypothesis that A. tsugae on lightly impacted trees are healthier than those on moderately impacted trees, this was not reflected in the population health measurements. Adelges tsugae egg health in response to tree health should be verified. This study provides the first examination of A. tsugae physiological health in relation to standard A. tsugae population health measures on hemlocks of different health levels. ; United States Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service [07-CA-11420004-161]; Virginia Tech [07-CA-11420004-161] ; The authors would like to thank T. Anderson for use of lab space and equipment, A. Reeves for preliminary assay development, A. Tanner for expertise with elemental analysis, and the many individuals who assisted with sample collection and measurements. We appreciate the Fishburn Experimental Forest, the University of Virginia Biological Station at Mt. Lake, and Twin Falls State Park, WV for their cooperation in completing this research on their property. This research was supported by cooperative agreement # 07-CA-11420004-161 between the United States Forest Service and Virginia Tech. ; Public domain authored by a U.S. government employee
Following the adventive arrival, subsequent spread, and ensuing impact of Adelges tsugae Annand (Hemiptera: Adelgidae), the hemlock woolly adelgid (HWA) in the eastern United States, a robust initiative was launched with the goal of decreasing ecosystem impacts from the loss of eastern hemlock (Pinales: Pinaceae). This initiative includes the use of biological control agents, including Laricobius spp. (Insecta: Coleoptera). Laboratory production of these agents is limited by subterranean mortality and early emergence. Therefore, the subterranean survivorship and timing of emergence of a mixture of Laricobius spp. was investigated. PVC traps internally lined with a sticky card and covered with a mesh screen were inserted into the soil to measure the percent emergence of adults based on the number of larvae placed within. The number of emerged adults in the field and laboratory-reared larval treatments was adjusted based on emergence numbers in the control and used as the response variable. Independent variables included in the final model were: treatment (field-collected vs. laboratory-reared), organic layer depth (cm), soil pH, and April-to-December mean soil moisture. No differences were found in survivorship between field-collected and laboratory-reared treatments. As pH and organic layer increased survivorship decreased, significantly. Although the majority of emergence occurred in the fall, emergence also occurred in spring and summer. The occurrence of spring and summer emergence and low survivorship (17.1 +/- 0.4%) in the field across all treatments suggests that these are characteristics of Laricobius spp. field biology in their introduced range and not artifacts of the laboratory rearing process. ; United States Department of Agriculture Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service [15-CA-11420004-0260] ; Published version ; We thank E. Lane, A. Hillen, R. Anderson, C. Jubb, and C. Preston for their technical assistance in the field and in the laboratory, and the University of Virginia's Mountain Lake Biological Station for allowing us to use their site. We would also like to thank the United States Department of Agriculture Forest Service for funding this work (15-CA-11420004-0260). ; Public domain authored by a U.S. government employee
Hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), has devastated eastern hemlock (Tsuga canadensis [L.] Carriere) in a major portion of its native range in eastern North America. Population dynamics of HWA in the absence of predators have been studied for decades. After many years and much effort directed towards rearing and releasing biological control agents to manage HWA, one of these agents, Laricobius nigrinus Fender (Coleoptera: Derodontidae), is now successfully established at significant densities at sites from the southern to the mid-Atlantic states of the eastern U.S. However, high densities of HWA still persist at many locations throughout the region and spread of HWA and associated damage to hemlock continues. Population models for HWA have suggested that even upwards of 90% predation on eggs laid by the overwintering sistens generation will have minimal effect in reducing the population densities of HWA, if HWA are at high density. In this study, we tested the ability of L. nigrinus to reduce HWA densities, and experimentally tested these model predictions to better understand what impact, if any, L. nigrinus has on HWA densities. By using predator exclusion cages at field sites with well-established populations of L. nigrinus, we were able to record HWA densities, fecundity, overwintering mortality, and predation by L. nigrinus, as well as the proportion of branch tips producing new growth on study trees. Using our field-collected data, we refitted the model in ways that allowed us to predict what population densities we could expect for the following summertime progrediens generation given previous HWA density and levels of L. nigrinus. In both years, we found that despite high rates (greater than 80% ovisac predation) of predation by L. nigrinus on uncaged branches compared to caged branches, there were no significant differences in subsequent densities of the HWA spring generation between caged and uncaged treatments, as predicted by our model. In 2018, our field-collected densities of the summer progrediens generation were lower than what was predicted by the model in both predator exclusion treatments, possibly due to the model not incorporating tree health and climatic factors. Simulation models of pest insect populations based on field-collected data such as fecundity, density, overwintering mortality, and predation, could prove to be important in informing researchers and managers about the role of the biological control agent in the population dynamics of the target host. ; USDA Forest Service, USA [14-CA-11420004-181] ; This work was funded by a cooperative agreement with the USDA Forest Service, USA (No. 14-CA-11420004-181). We thank R., Reardon, N. Schneeburger, R. Rhea of the Forest Service for arranging and administrating our funding, M. Meyer for helping us find field sites in NJ and R. Mays, A. Dechaine (Virginia Tech) and B. Mudder (USDA Forest Service) for helping collect samples from the field. We thank A. Roehrig, A. Langevin for processing samples. We thank H. Broadley, J. Anderson, and B. Padilla for help with statistical analysis and graphics. We thank J. Chandler, R. Van Driesche, and D. Orwig for reviewing earlier drafts of this MS. ; Public domain authored by a U.S. government employee
Hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is an invasive pest causing significant mortality to eastern and Carolina hemlock in eastern North America. Since 2003, management of HWA has included targeted release of the HWA predator Laricobius nigrinus Fender (Coleoptera: Derodontidae), native to western North America. Establishment of L. nigrinus at release sites is well documented, but investigations of its impact on HWA populations have been limited. A four-year (2014-2018), two-phase study using predator exclusion cages to assess the impact of L. nigrinus on HWA was conducted at nine previous release sites in the eastern United States. Significantly more HWA sistens ovisacs were disturbed on no-cage and open-cage branches than on caged branches where predators were excluded. Mean disturbance levels on cage, no-cage and open-cage branches was 8, 38, and 27 percent, respectively. Seven of nine sites had a mean HWA ovisac disturbance greater than 50% for at least one year. Winter temperatures were also a significant factor in overall mortality of the sistens generation with a mean of 46% on study branches. Six of nine sites had a mean overall mortality (winter mortality and predation) greater than 80% for at least one year. Larvae of Laricobius spp. were recovered at all sites during this study. Sequencing of the COI gene from recoveries in Phase One (2015 and 2016) indicated that 88% were L. nigrinus and 12% were L. rubidus LeConte. Microsatellite analysis performed during Phase Two (2017 and 2018) indicated that approximately 97% of larval recoveries were L. nigrinus, 2% were hybrids of L. nigrinus and L. rubidus, and 1% were L. rubidus. Results of this study suggest that L. nigrinus can significantly impact the HWA sistens generation ovisacs and continued investment in the use of this species as a biological control is recommended. ; USDA Forest Service cooperative agreementUnited States Department of Agriculture (USDA)United States Forest Service [14-CA-11420004-028] ; We gratefully acknowledge the assistance of Dr. Thomas Kuhar and Dr. Douglas Pfieffer (Virginia Tech) for review of this project, as well as Dr. Carlyle Brewster (Virginia Tech) for assistance with data analysis. We thank Dr. Nathan Havill (USDA Forest Service), Kari Stanley (Virginia Tech), and Melissa Fischer (Washington State Department of Natural Resources) for assistance with molecular protocols, as well as Mark Mayer (New Jersey Department of Agriculture), Scott Passwaters (James River State Park), Biff Thompson (Maryland Department of Agriculture), Jesse Webster (Great Smoky Mountains National Park), and the staff at Blackberry Farm (Tennessee) for site assistance. Thank you to Arthur Morgan School, Celo Community, and the Chattahoochee National Forest for permission to use sites in NC and GA. We are grateful to Natalie Morris, Kara Jeffries, Andy Dechaine, Ryan Mays, Ashley Toland, and James Wahls (Virginia Tech), Bryan Mudder and Andrew Tait (USDA Forest Service), David Bechtel, Philip Hensley, Elizabeth McCarty, Forest Palmer, Pat Parkman, and David Paulsen (University of Tennessee), and Peter Menzies, Marika Lapham, and Ivy Haas (University of North Carolina Asheville), for laboratory and field assistance. This work was funded under USDA Forest Service cooperative agreement 14-CA-11420004-028. ; Public domain authored by a U.S. government employee
