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Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is a species of wood boring beetle which feeds on the inner bark of ash trees, Fraxinus spp., and white fringe tree, Chionanthus virginicus L. In North America emerald ash borer feeding damages the trees vascular system, killing the tree in 1-6 years after initial infestation. Emerald ash borer's native range is north east China, the Russian Far East, and the Korean peninsula. In the mid-1990s emerald ash borer was accidentally introduced to Michigan from the Hebei and Tianjin city province regions of China. Since then, due to human-aided transport and natural spread, emerald ash borer now infests 35 states and five Canadian provinces. Studies in to Asia discovered several species of parasitic wasps which feed and reproduce on emerald ash borer; four of these species were approved for release in the United States. Three species which attack emerald ash borer larvae Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), Spathius agrili Yang (Hymenoptera: Braconidae), and Spathius galinae Belokobylskij and Strazanac (Hymenoptera: Braconidae), and one species which utilizes emerald ash borer eggs, Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae). This research focuses on the control of emerald ash borer using the three larvae-utilizing species of parasitic wasp. The first objective of this research focuses on the synchrony of emerald ash borer larvae with the early spring emergence of S. agrili and S. galinae. The first objective also assessed how two different cold temperature treatments changed the emergence timing, and health of the wasps. The second objective assessed to determine the effects of competition between S. agrili and S. galinae when they were exposed to a single emerald ash borer larvae sequentially, and simultaneously. When exposed sequentially, the first wasp held the competitive advantage, but when exposed simultaneously S. agrili had a small advantage, but did not completely exclude S. galinae. The third objective focused on the potential for two larval parasitoids, S. agrili and S. galinae to parasitize emerald ash borer larvae in the novel host plant white fringe tree. We determined that both parasitoids are capable of finding and parasitizing emerald ash borer larvae within a non-ash host. Finally, we located 13 stands of emerald ash borer infested ash in Virginia and North Carolina in order to determine its life cycle, and overwintering life stage. We determined that emerald ash borer overwinters at different life stages, and has a more complex life cycle than previously reported. Additionally, all three species of larvae-utilizing parasitic wasp were recovered at field sites at least 1 year after release. These results all show promise for the biocontrol program, and indicate that biocontrol of emerald ash borer could be successful in Virginia and North Carolina. / Doctor of Philosophy / Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is a wood boring beetle which feeds on the inner bark of ash trees, Fraxinus spp., and white fringe tree, Chionanthus virginicus L. In the mid-1990s emerald ash borer was accidentally introduced to Michigan from the Hebei and Tianjin city province regions of China. Since then, due to human-aided transport and natural spread, emerald ash borer now infests urban and natural forests in 35 states and five Canadian provinces. North American ash trees did not evolve with emerad ash borer, and have little resistance to their attack. A North American ash or white fringe tree attacked by emerald ash borer dies in 1-6 years if left untreated. Systemic insecticide treatments exist, but require annual treatment and are less effective than initially hoped. Additionally, systemic insecticides are impractical to apply to forest ecosystems. Researchers traveled to the Asia, and discovered several species of parasitic wasps which attack emerald ash borer. After years of efficacy and host-exclusivity testing four species were released in the United States. Three species which exclusively utilize emerald ash borer larvae Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), Spathius agrili Yang (Hymenoptera: Braconidae), and Spathius galinae Belokobylskij and Strazanac (Hymenoptera: Braconidae), and one species which utilizes emerald ash borer eggs, Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae). My research focuses on the control of emerald ash borer using the three larvae-utilizing species of parasitic wasp. Chapter two focuses on the life cycle of emerald ash borer larvae, S. agrili and S. galinae during the early spring. We determined that both parasitoid species have similarly timed life cycles as EAB, indicating a good climate match in Virginia. Chapter three describes the interactions between S. agrili and S. galinae when competing for EAB larvae. We determined that the first species to attack the larvae has the advantage; and when adult wasps competed to find a larvae neither species completely dominated the other. The third objective focused on the potential for two larval parasitoids, S. agrili and S. galinae to parasitize emerald ash borer larvae in the novel host plant white fringe tree. We determined that both parasitoids are capable of finding and parasitizing emerald ash borer larvae within white fringe tree. Finally, we located 13 stands of emerald ash borer-infested ash in Virginia and North Carolina in order to determine its life cycle, and overwintering life stage. We determined that emerald ash borer overwinters at different life stages, and has a more complex life cycle than previously reported. Additionally, all three species of larvae-utilizing parasitic wasp were recovered at field sites at least 1 year after release. These results all show promise for the biocontrol program, and indicate that biocontrol of emerald ash borer could be successful in Virginia and North Carolina.

Currently, there is little known about stink bug (Hemiptera: Pentatomidae) eggs, their natural enemies, and their susceptibility to insecticides. A survey of stink bug egg parasitoids was conducted in row crops and vegetables in eastern Virginia. Parasitization was highest in Euschistus servus (Say) with 89.7% and 49.2% of egg masses and individual eggs parasitized, respectively, followed by Acrosternum hilare (Say), with nearly half of all individual eggs parasitized. The most common parasitoid was Telenomus podisi Ashmead (Hymenoptera: Scelionidae). Laboratory egg-dip bioassays and field applications of acephate, lambda-cyhalothrin, spinosad, and thiamethoxam, were carried out to determine efficacy against nonparasitized E. servus and A. hilare eggs, and T. podisi embryos developing in E. servus eggs. Results showed that eggs of both species were susceptible to insecticides, that there was little difference among insecticides, but there was generally greater mortality in field-treated versus dipped eggs. Developing T. podisi were generally more susceptible to insecticides than stink bugs. Scanning electron microscopy was used to investigate oviposition sites as possible sites of insecticide movement into eggs. Oviposition wounds and holes made by a tungsten probe were similarly sealed by a "scab", so it was not clear whether these wounds allow for increased insecticide movement into parasitized eggs. Differences in chorion permeability of non-parasitized and parasitized eggs were compared by immersing them in solutions containing different ¹⁴C-ammended insecticides at field application rates for 0, 30, 120 or 240 minutes. Results showed that insecticide movement into the egg increased significantly with immersion time for both acephate and λ-cyhalothrin, but there were no significant differences between nonparasitized and parasitized eggs. Neither immersion time nor egg status was significant for thiamethoxam. A model was constructed that predicts amount of insecticide entering the egg at any given time. An 8-week survey for the brown marmorated stink bug, Halyomorpha halys (Stål) was conducted in Beijing and five other cities in China. Incidence of egg parasitism was recorded. Results showed that H. halys utilized at least four different plants throughout the summer, and insects were found in Nanjing, Kunming, and Xi'an. Parasitization of eggs was noted, and the parasitoids were identified as Trissolcus halyomorphae Yang (Scelionidae: Hymenoptera) by K.A. Hoelmer (USDA-ARS). / Ph. D.

Predation, egg production and survivorship of Laricobius nigrinus Fender, L. rubidus, LeConte, and L. osakensis Montgomery and Shiyaki (proposed), predators of hemlock woolly adelgid, Adelges tsugae, Annand, were investigated in the laboratory and in the field. In individual assays, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. When all three species were together, the numbers of ovisacs preyed upon were similar to the mean of all three individual species. Adult predators fed on few eggs and did not exhibit any species preference. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, predators were enclosed in sleeve cages with both high (> 120 ovisacs) and low (< 90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly higher at the high prey-density than at the low prey-density. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to co-exist and can be in the same location for biological control of A. tsugae. / Master of Science in Life Sciences

Arthropod natural enemies play a key role in controlling potentially damaging pest populations in agroecosystems. An abundant and diverse natural enemy community is associated with higher yields in a variety of crops. Certain aspects of soybean production can make a field more or less amenable to a robust natural enemy community. For instance, commonly used broad-spectrum insecticides which are highly toxic to most arthropods can decrease natural enemy densities and allow for secondary pest outbreaks. Selective insecticides that have less impact on natural enemy populations allow for pest control while preserving important predators. Another production decision that could alter natural enemy communities is the choice of cropping system, specifically planting early (full season) or late, after small grain harvest (double crop). My research objectives were to examine how 1) selective insecticides and 2) cropping system affect the density and diversity of natural enemies in Virginia soybean. To address the first objective I compared the natural enemy community in soybean plots that were exposed to selective insecticides, broad-spectrum insecticides or no insecticide. I sampled insects using three different techniques and found that the two selective insecticides I tested, both from a new class called diamides, did not reduce the natural enemy community compared to controls. To examine how cropping system affects the natural enemy community I sampled full season and double crop fields during the growing season for two years. In 2014 ground-dwelling spider diversity was higher in full season soybean. In both years, double crop soybeans had higher abundance of spiders and insect natural enemies on the ground and in the foliage compared with full season soybean. This was unexpected, since double crop soybeans are planted later than full season and arthropod populations would have less time to colonize and grow. When I compared diversity of a family of predatory beetles I found higher diversity in full season soybean. The similarity in spider and insect natural enemy diversity and abundance trends suggests that a greater number of species can co-exist in full season soybean, while in double crop soybeans a few dominant natural enemies thrive. / Ph. D.

This study evaluates the economic feasibility of a biological control industry in Niger. Farmers in the Sahel region of Niger are vulnerable to high millet yield losses due to the millet head miner, and their pest control options are extremely limited. Researchers have begun to support small businesses which sell a beneficial insect (Habrobracon Hebetor) that is very effective in limiting millet yield losses due to the millet head miner. This study discusses a wide range of questions related to the economic prospects of these businesses using two main analytical methods, an economic feasibility assessment and an econometric analysis. The economic feasibility assessment provides budget analysis for the potential businesses and discusses business options for scaling, price setting, and organizing. A central question in this analysis is whether farmers can cooperatively purchase beneficial insects as a means of preventing free-riding. With free-riding as a prominent concern for businesses, this study also provides an econometric analysis of the factors that affect farmer's willingness-to-pay for beneficial insects. / Master of Science

The hemlock woolly adelgid (HWA) Adelges tsugae (Annand) (Hemiptera: Adelgidae), has spread throughout most of the range of eastern hemlocks, Tsuga canadensis (L.) and the entire range of Carolina hemlocks, Tsuga caroliniana (Engelman) in eastern North America. Forest managers often implement an integrated pest management (IPM) strategy that combines chemical, silvicultural, and biological control tactics to create a more sustainable and effective approach for managing HWA. Laricobius spp. (Coleoptera: Derodontidae) are the primary biological control agents within IPM scenarios for HWA. Imidacloprid (IMI), the most widely used insecticide for HWA management, is typically applied to the soil below HWA infested trees and breaks down into several metabolites, including two with insecticidal properties; 5-hydroxy imidacloprid (5H-IMI) and imidacloprid-olefin (IMI-OLE). Imidacloprid-olefin is known to be up to 14 times as lethal to HWA as IMI and is produced as imidacloprid is first hydroxylated into 5H-IMI and further metabolized into IMI-OLE. Because Laricobius spp. spends half of its life in aestival diapause in soil below HWA infested trees, there is the potential for these biological control agents to encounter toxic residues within an IPM setting. Imidacloprid and its metabolites are known to cause mortality in Laricobius spp. feeding on HWA from previously treated trees, but the impact of soil applied imidacloprid on their subterranean survivorship has not been studied. Furthermore, there is limited knowledge on the subterranean portion of Laricobius spp. life cycle. The first study determined the depth to which Laricobius spp. burrowed during their subterranean life phase using 3D X-ray microscopy. When held in containers with two differing soil compaction intensities, 0.2 kg/cm2 and 0.5 kg/cm2, Laricobius spp. were found to burrow an average (± SE) of 2.7 ± 1.5 cm and 1.4 ± 1.3 cm deep, respectively. The second study assessed the effect of three different imidacloprid soil treatments; soil injection, soil drench and CoreTect tablets, on the subterranean survivorshiop of Laricobius spp. The soil drench application technique applied in fall 2020 consistently resulted in significantly higher IMI, 5H-IMI, and IMI-OLE residues than the other two treatments over both years of this study (2021 and 2022). The soil injection treatments from both 2020 and 2017 resulted in above average field emergence of beetles in 2021 and 2022, with relatively insignificant residue quantities present. This study suggests that the soil injection treatment method provides a lower level risk of metabolite exposure to Laricobius spp. compared to soil drench and CoreTect tablet imidacloprid application methods. / Master of Science in Life Sciences / In eastern North America, there are two species of hemlock trees whose longevity and unique shade tolerant adaptations are important to the ecosystems within which they are found. Eastern hemlocks range from southeastern Canada to the southern Appalachian Mountains, while Carolina hemlocks are restricted to the southern Appalachians from northern Georgia to Virginia. Since its first formal identification in Richmond, VA in 1951, the hemlock woolly adelgid (HWA) has caused widespread damage and mortality throughout much of the range of eastern hemlocks and the entire range of Carolina hemlocks. HWA consumes nutrients and restricts water flow within the tree, eventually leading to tree mortality. Forest managers typically rely on an integrated approach, that combines chemical applications with the simultaneous release of insects that naturally attack HWA on untreated trees within the same forest setting. Imidacloprid is the most widely used insecticide for HWA management and is typically applied to the soil below HWA infested trees. This insecticide is absorbed through the roots and travels through the tree where HWA feed and die as a result. Laricobius spp., the primary insect consuming HWA on infested trees, spends part of their life in a below ground summer dormancy. Imidacloprid and its secondary compounds are known to cause mortality in Laricobius spp. feeding on HWA from treated trees, but the impact of soil applied imidacloprid on their below ground survivorship has not been studied to date. Furthermore, while extensive studies have taken place to understand the biology of Laricobius spp., there is limited knowledge about their dormant state. In one study, the depth to which Laricobius spp. burrowed during their below ground life phase was determined using 3D X-ray microscopy. In a second study, the effect of three common imidacloprid treatments; soil injection, soil drench, and CoreTect tablets, on below ground survivorship was examined. Laricobius spp. were found to burrow an average (± S.E.) of 2.7 ± 1.5 cm and 1.4 ± 1.3 cm deep in soil compacted at 0.2 kg/cm2 and 0.5 kg/cm2, respectively. Chemical residue quantities were greatest in soil treated with soil drench in fall 2020, and were found to significantly impact Laricobius spp. survival. Overall, survival was the lowest from the soil treated with CoreTect tablets in 2020. Surival was the greatest from soil that received soil injection treatments in both 2020 and 2017 and had relatively insignificant imidacloprid residues present where the insects typically occur in the soil. Findings from this study suggest that imidacloprid application using the soil injection method is a less risky technique for chemical control in an IPM setting when compared to soil drench and CoreTect methods.

The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae) is a small, non-native insect that feeds on hemlock (Tsuga spp.) species native to the eastern United States. One biological control agent, Laricobius osakensis, shows promise due to its voracious feeding on and synchronous life cycle with HWA. This beetle species is originally from Japan and has undergone all the necessary testing while in quarantine, gaining permission for field release in 2010. Field releases began in the fall of 2012 and continued the following fall. Reproduction occurred at the first year's field sites with beetles recovered at both sites the following fall. During the second year of field work, beetle recovery was low due to winter temperatures that caused high HWA mortality. All of the L. osakensis beetles released in the field are first reared in an Insectary on Virginia Tech's campus. To improve health of these beetles during rearing, a series of chemical amendments were added to the water baths where HWA infested cut hemlock branches were placed. HWA samples were taken from each treatment and analyzed for carbon, nitrogen and total carbohydrates and beetles emergence was recorded in relation to prescribed treatment. None of the treatments appeared as the best for improving HWA health, but there were differences between the sampling months within the two years. These differences in month correlate with the biological processes occurring within HWA at these times such as reproduction and preparation for aestivation. No treatment helped increase beetle emergence. / Master of Science in Life Sciences

Outbreaks of spider mites (Acari: Tetranychidae) in vineyards have been increasing with the expansion of the industry in Virginia. Only three effective acaricides are registered on grapes and as resistance begins to occur, control options are limited. Biological control of spider mites by inoculative or inundative releases of predatory mites has been tried on a wide range of crops including grapes. This project examined the feasibility of using <i>Neoseiulus fallacis</i> (Acari: Phytoseiidae) as a potential large-scale biological control agent in vineyards. Slide dip bioassays were conducted on <i>N. fallacis</i> to determine the toxicity of insecticides, fungicides and herbicides commonly used on grapes in Virginia. In addition to laboratory experiments, commercially obtained <i>N. fallacis</i> were released in vineyards with spider mite infestations. The populations of both mites were then monitored on a regular basis to determine dispersal and distribution patterns. Among the insecticides tested in the laboratory bioassays, carbaryl, azinphos-methyl, phosmet, cyhexatin, and pyridaben all caused significantly higher mortality than the control treatment. Fungicides tested were not toxic to the predator, but three herbicides caused high mortality. Glufosinate caused 100% mortality after 24 hours and both oxyfluorfen and paraquat had adverse effects on <i>N. fallacis</i>. The use of materials that were found to be toxic to the predator would not be compatible with inoculative releases of <i>N. fallacis</i>. Field release results were variable. Three releases were made in 1999 and 2000., Recovery of the predator was low following the releases at two of the sites, probably due to lack of prey. At the third site enough predators were recovered to analyze the spatial distribution of the predator and prey populations. It appears that there is no similar aggregation pattern between the predator and prey at the same point in time although there is an indication of the predator spreading is response to the prey distribution. A more complete season of sampling would give more conclusive evidence of this trend. Although the distribution of the two populations were dissimilar, the predator was present throughout the season and did spread through the entire plot indicating that the predator may be able to colonize the vineyard if it successfully overwinters. / Master of Science

Grass carp Ctenopharyngodon idella have been stocked throughout the world due to their utility as a biological control. In the United States, the species has been used to successfully control invasive, aquatic weeds such as hydrilla Hydrilla verticillata. Despite the large body of research surrounding the use of grass carp, few studies have demonstrated widely applicable methods for evaluating the success of weed control based on grass carp behavior and population dynamics. Classic methods of biological control using grass carp often rely on a single, large stocking of fish. Few of these studies have demonstrated success in achieving intermediate levels of weed control. Managers would be better equipped to make decisions regarding stocking and maintenance grass carp populations with better information about behavior, survival, and population structure. Improved decision making could result in reduced cost and increased effectiveness of stocking. In order to examine current knowledge gaps for management, I investigated the movements and habitat use of grass carp, post-stocking survival, age-specific survival rates, and population dynamics of grass carp in Lake Gaston, North Carolina and Virginia. I characterized relationships between grass carp behavior and environmental factors using radio-telemetry. The average rate of movement for grass carp in Lake Gaston was about 137 m/d. Rapid dispersal after stocking was followed by long periods of no movement. However, when time after stocking was held constant in models of behavior, fish moved about 200 m/d more in the second year after stocking than in the first year, and were found closer to shore. On average, grass carp were found about 40 m from shore in about 2.5-3.5 m of water, although mean depth of water at grass carp locations varied seasonally, being shallowest in summer and deepest in winter. Although depth of water at grass carp locations did not vary by stocking location, Grass carp were found closer to shorelines in the upper reservoir than in the lower reservoir. I found significant relationships between grass carp behavior and hydrological processes such as lake elevation and dam releases in the reservoir, as well as with other environmental factors such as water temperature, photoperiod, and weather conditions. The results of this study should be useful in better understanding how behavior can affect management decisions. Specifically, grass carp behavior appears to change with age and environmental conditions within large reservoir systems. Future research should focus more closely on the effects of large-scale flow dynamics on grass carp behavior. I estimated age-1 survival of grass carp from mark-recapture models designed for radio-tagged animals, and characterized relationships between age-1 survival and factors under the control of management, such as stocking locations and size at stocking. . According to the most-plausible model developed in this study, survival of age-1 grass carp in Lake Gaston varied throughout the year, and the probability of an individual grass carp surviving to the end of its first year (±SE) was 0.57(±0.10). According to the second-most-plausible model developed in this study, grass carp survival varied between stocking locations, and was twice as high in the upper reservoir (0.87±0.09) than in the lower reservoir (0.43±0.11). The differences in survival between stocking locations suggest that the cost-effectiveness of grass carp stocking could be improved by focusing stocking efforts in specific regions of Lake Gaston. Furthermore, none of the models developed in this study that incorporated the effects of size (length and weight) or condition factor accounted for a meaningful amount of the total model weights. These results suggest that costs of grass carp stocking could be reduced in Lake Gaston by using a smaller minimum size (352 mm, TL) than is commonly referred to in the literature (450 mm, TL). I used grass carp collected by bowfishers in Lake Gaston to characterize the age, growth, and survival of grass carp in the system. From these data, I characterized relationships between fish population dynamics and annual hydrilla coverage. Grass carp collected from Lake Gaston ranged in age 1-16 years. Growth of grass carp in Gaston was described by the von Bertalanffy growth function as Lt = 1297(1-e -0.1352 (t+1.52)). I estimated mortality from the von Bertalanffy growth parameters using methods based on growth, temperature, and age; and with each mortality estimate I estimated population size and standing biomass of grass carp. Use of age-specific mortality rates produced lower estimates of grass carp numbers and standing biomass in Lake Gaston than did the use of a single, instantaneous mortality rate for all ages. I determined that growth of grass carp slowed considerably after the fourth year and that slowed growth, in combination with changes in mortality, resulted in a decrease in the amount of hydrilla controlled by a given cohort after four years in Lake Gaston. This phenomenon resulted in an approximately linear relationship between the biomass of grass carp at year i and hectares of hydrilla at year i+3. Based on this relationship, I predicted that the biomass of grass carp necessary to reduce hydrilla coverage to the target level of 120 ha in Lake Gaston is about 91,184 kg (±38,146 kg) and that the current biomass of grass carp in Lake Gaston is about 108,073 kg (±3,609 kg). I conclude that grass carp biomass is at or near levels that should reduce hydrilla coverage to 120 ha between 2013 and 2018. This research provides an effective means for synthesis of information that is critical to understanding sterile, triploid grass carp populations when assumptions of other methods cannot be met. The results of this study should be of immediate utility to hydrilla management efforts in Lake Gaston and other systems. Furthermore, the age-specific mortality rates developed in this study should be useful as starting values for grass carp management in similar systems. / Master of Science