The biology and host-specificity of <i>Laricobius kangdingensis</i> sp. n. (Coleoptera: Derodontidae), a new predator of hemlock woolly adelgid (HWA), <i>Adelges tsugae</i> Annand (Homoptera: Adelgidae) were investigated and compared with that of a related predator of HWA, <i>L. nigrinus</i> Fender. Adults became active in June 2003; the males emerged first and in greater numbers than the females. The sex ratio of female to male was 1: 1.1. <i>Laricobius kangdingensis</i> sp. n. has four larval instars. The total number of eggs laid between 7 July 2003 and 7 August 2004 was 1327. Mean lifetime fecundity per female was 196.4 ± 53.4 eggs and 97.9 eggs for the P1 (parental gen.) and F1 generations, respectively. In comparison, lifetime fecundity for F1 <i>L. nigrinus</i> was 100.8 ± 89.6 eggs. Developmental rates were studied in fall 2003 and spring 2004. Combined with data gathered previously at 12 and 15ºC in early 2003, the 6, 9, and 18ºC data were used to determine lower temperature development thresholds for the egg (2.8ºC), larval (1.6ºC), and pre-pupal (5.8ºC) stages. The egg and larval thresholds are lower than those observed for <i>L. nigrinus</i>. <i>Laricobius kangdingensis</i> sp. n. individuals completed development only at 12 and 15ºC; however, these adults did not emerge from aestivation after pupation. <i>Laricobius kangdingensis</i> sp. n. appears to be host-specific. In paired-choice feeding tests, adults consumed significantly more HWA than two other adelgid species [eastern spruce gall adelgid, <i>Adelges abietis</i> (L.), and pine bark adelgid, <i>Pineus strobi</i> (Hartig)], the pine needle scale, <i>Chionaspis pinifoliae</i> (Fitch), and the woolly alder aphid, <i>Paraprociphilus tessellatus</i> (Fitch). In paired-choice oviposition tests, females laid more eggs on HWA-infested eastern hemlock than on any other test prey. In no-choice host suitability experiments larvae fed on HWA; eastern spruce gall adelgid; the larch adelgid, <i>A. laricis</i> Vallot; the balsam woolly adelgid, <i>A. piceae</i> (Ratzeburg); pine bark adelgid; and pine needle scale, but not on woolly alder aphid or elongate hemlock scale, <i>Fiorinia externa</i> Ferris. Although no larvae completed development in any of the bioassays, 6 out of 15 larvae (40%) in the HWA treatment reached the pre-pupal stage. One larva out of 6 reached the pre-pupal stage on pine bark adelgid. / Master of Science

The hemlock woolly adelgid (HWA), Adelges tsugae Annand, is an invasive pest of eastern hemlock, Tsuga canadensis (L.) Carriere and Carolina hemlock Tsuga caroliniana Englem. in the eastern United States. A newly reported beetle predator for HWA, Scymnus (Pullus) coniferarum Crotch (Coleoptera: Cocinellidae) preys on the pest in the western United States, and was approved for release in the eastern United States for the control of HWA. This research investigated the viability of S. coniferarum as a biological control agent of A. tsugae in the eastern United States, as well as the ecological dynamics between S. coniferarum and host prey species in its native range of western North America. In objective one, S. coniferarum predation, reproductive potential, and survival were evaluated in field-cages on adelgid infested T. canadensis in southwestern Virginia. Adult S. coniferarum fed on both generations and all life stages of A. tsugae at rates comparable to other adelgid-specific predators, and survived for extended periods of time in the field. In objective two, host-range tests for S. coniferarum were conducted in a series of no-choice and paired-choice feeding, oviposition, and development studies. Scymnus coniferarum adults fed on all adelgid species, and completed development on HWA and Adelges piceae Ratz. Scymmnus coniferarum oviposition was extremely low. In the final objective, Douglas-fir, Pseudotusga menziesii Mirb., Shore pine, Pinus contorta Dougl., western white pine, Pinus monticola Dougl., and western hemlock, Tsuga heterophylla (Raf.) Sarg. host tree species were sampled in Tacoma, Washington to investigate the life history of S. coniferarum and associated adelgid prey species in the western United States. Scymnus coniferarum adults were found on both pine species, Douglas fir, and western hemlock, and seemed to move between host tree species seasonally. Each host tree supports a different adelgid species, and a limited diet of strictly HWA in host-range tests could have contributed to low oviposition rates. This study suggested that S. coniferarum is a voracious predator of HWA in the field and laboratory. However, S. coniferarum laid very few eggs in laboratory studies, and zero eggs were recovered in field-cage analyses. This suggested that S. coniferarum may rely on multiple adelgid species to reproduce and establish in the eastern United States. / Ph. D. / Biological control is an economically and environmentally logical approach to pest management, through the introduction of a natural enemy or predator. This dissertation investigated the potential of Scymnus (Pullus) coniferarum as a biological control agent of the invasive pest species, hemlock woolly adelgid, otherwise known as HWA. The hemlock woolly adelgid is an invasive pest insect in the eastern United States, responsible for causing widespread death of eastern hemlock trees from southern Maine to Georgia. Scymnus coniferarum is a lady beetle that preys on HWA in the western United States, part of HWA’s native range. In objective one, S. coniferarum predation, reproductive potential, and survival were evaluated in field-cages on HWA-infested eastern hemlock trees in southwestern Virginia. Adult S. coniferarum beetles fed on HWA year-round, at a rate comparable to other successful biological control agents. In objective two, S. coniferarum beetles were confined to a selection of insect species similar to HWA and native to the eastern United States. Scymnus coniferarum predation, oviposition and development was observed in these tests in order to assess the potential impact of S. coniferarum on non-target species in the eastern United States. Scymnus coniferarum beetles fed on all adelgid species, and successfully laid eggs and developed to adults while feeding on the balsam woolly adelgid, another pest species in the eastern United States. Adult beetles laid very few eggs, and were very difficult to rear in a laboratory setting. In the final objective, Douglas-fir, Shore pine, western white pine, and western hemlock trees were sampled in Tacoma, WA to investigate the life history of S. coniferarum and other adelgid prey species in the western United States. Scymnus coniferarum adults were found on every species of sample tree except for Douglas-fir, and seemed to move among host trees seasonally. Host tree species support different adelgid species, and a limited diet of strictly HWA in host-range tests could have contributed to low oviposition rates. The lady beetle S. coniferarum was a voracious predator of HWA in field and laboratory studies. However, S. coniferarum laid very few eggs in laboratory studies, and zero eggs were recovered in field-cage analyses. This suggested that S. coniferarum may rely on multiple adelgid species to reproduce and establish in the eastern United States. This had either positive or negative implications regarding its viability to establish, flourish, and impact HWA in the eastern United States.

The insecticide imidacloprid, has been found to be highly effective in suppressing hemlock woolly adelgid, Adelges tsugae. Laricobius nigrinus is a predatory beetle released as a biological control of adelgids in the eastern U.S. This project was designed to develop a pest management strategy that utilizes both tactics concurrently within the same site. It will assess the efficiency of this strategy in reducing HWA populations and improving the health of hemlock forests. The project was started in 2010 and data were collected annually through 2016. The project spanned three sites in three different states (KY, WV, and TN). Results show that tree health has generally declined across all sites for each year. HWA population index values are highly variable and are more strongly influenced by the occurrence of low winter temperatures than by treatment effect. Cross-correlation analysis of tree health and HWA population, revealed characteristics of their temporal relationship. In two of the three sites, tree health lagged up to three years behind changes in HWA population, and HWA populations lagged approximately one year behind changes in tree health. L. nigrinus did not establish at any site as of 2016. The lack of sustained recovery of the beetle may be attributable to the occurrence of extremely cold temperatures during the winters of 2014 and 2015 which produced subsequent crashes in the HWA population at two of the three sites. In TN, the L. nigrinus population may have never established due to a decline in the HWA population shortly after release. / Master of Science in Life Sciences / The insecticide imidacloprid, has been found to be highly effective in suppressing hemlock woolly adelgid, <i>Adelges tsugae. Laricobius nigrinus</i> is a predatory beetle released as a biological control of adelgids in the eastern U.S. This project was designed to develop a pest management strategy that utilizes both tactics concurrently within the same site. It will assess the efficiency of this strategy in reducing HWA populations and improving the health of hemlock forests. The project was started in 2010 and data were collected annually through 2016. The project spanned three sites in three different states (KY, WV, and TN). Results show that tree health has generally declined across all sites for each year. HWA population index values are highly variable and are more strongly influenced by the occurrence of low winter temperatures than by treatment effect. Cross-correlation analysis of tree health and HWA population, revealed characteristics of their temporal relationship. In two of the three sites, tree health lagged up to three years behind changes in HWA population, and HWA populations lagged approximately one year behind changes in tree health. <i>L. nigrinus</i> did not establish at any site as of 2016. The lack of sustained recovery of the beetle may be attributable to the occurrence of extremely cold temperatures during the winters of 2014 and 2015 which produced subsequent crashes in the HWA population at two of the three sites. In TN, the <i>L. nigrinus</i> population may have never established due to a decline in the HWA population shortly after release.

Insects form close partnerships, or symbioses, with bacteria. These partnerships allow the insects to use resources that would be unavailable to them otherwise. Certain insects, hemipterans, are able to feed on nutrient-poor plant-sap because these bacteria supplement their diets. While this association is beneficial for both the insect and bacteria, it also comes with consequences: the genomes of bacterial symbionts typically undergo extreme degradation, becoming small and lacking many genes necessary for typical bacterial functioning. In the Hemiptera, aphids, mealybugs, cicadas, true bugs,and their relatives, these bacterial partnerships tend to be stable over millions of years. However, adelgids (Aphidoidea: Adelgidae) are highly unusual in that their symbiotic bacteria have been frequently replaced. These replacements offer a unique opportunity to explore the effects of symbiont role and age on symbiont genome degradation. My dissertation uses the pattern of adelgid symbiont gains and losses to understand the process of symbiont replacements and co-symbiont gain. I accomplished this by sequencing and annotating the genomes of adelgid symbionts from across the family, first focusing on the symbionts from a pest species, then expanding to representatives from across the family, and finally conducting an in-depth exploration of how the genomes of a symbiont found in two branches of the adelgids varies between species. Through this work I demonstrate that adelgid symbionts are nutritional providers, they have a unique pattern for distributing the work of providing nutrients between the symbiont pairs, and that a symbiont’s precedence, whether it was there first or whether it joined another symbiont, has an impact on genome degradation.

Eastern hemlock (Tsuga canadensis) is in decline because of infestation by the invasive hemlock woolly adelgid (Adelges tsugae; ‘HWA’) and, to a lesser extent, the elongate hemlock scale (Fiorinia externa; ‘EHS’). Many conifers respond to insect herbivory by inducing oleoresin-based defenses, however it is unknown whether eastern hemlock is capable of this inducible response. We conducted a plantation setting study of artificially infested saplings to determine if feeding by HWA or EHS induces changes in the tree’s volatile chemistry. The induced changes in volatiles we found were unlike the terpenoid-based defenses of related conifers. Only HWA feeding elevated methyl salicylate, a plant signal for systemic acquired resistance, and benzyl alcohol, a known antimicrobial and aphid deterrent. The influence of environmental conditions and tree life-stage on hemlock volatile chemistry, potentially important factors for wild hemlock populations, is unknown. We investigated whether mature and immature forest trees respond to HWA infestation with the same patterns of volatile production as plantation saplings in full sun and amended soils. HWA induced volatile changes comparable to those of plantation saplings, with many-fold benzenoid increases and no terpenoid-based resinosis. Nearly all volatiles were substantially more abundant in forest than plantation trees, suggesting the effect of site conditions should be addressed in investigations of mechanisms operative in HWA-resistant biotypes of eastern hemlock. Our findings represent the first important step toward understanding the influence of inducible phytochemical responses on hemlock susceptibility to exotic pests, and highlight the possibility of salicylic acid-dependent biosynthetic activity in this gymnosperm system.

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