Assessment of Factors Affecting Establishment of Biological Control Agents of Hemlock Woolly Adelgid on Eastern Hemlock in the Great Smoky Mountains National Park
Date of Award
Doctor of Philosophy
Plants, Soils, and Insects
Jerome F. Grant
Paris Lambdin, David Buckley, Frank Hale
Eastern hemlock in the Great Smoky Mountains National Park (GRSM) is threatened by hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae). To manage this invasive pest in GRSM, ca. 550,000 Sasajiscymnus tsugae (Sasaji and McClure) (Coleoptera: Coccinellidae) and 7,857 Laricobius nigrinus Fender (Coleoptera: Derodontidae) have been released. Limited information is available on their establishment in GRSM. To fill this gap, a study was initiated to assess establishment of these predators and their impact on hemlock health. To determine factors affecting establishment of these predators, 65 release sites were sampled from 2008 to 2012. Several factors were evaluated for their association with establishment and recovery of S. tsugae. Predatory beetle release information, topographic features, and temperature data were obtained from GRSM personnel. These factors were evaluated using stepwise logistic regression and Pearson correlation. High resolution digital imagery was used in conjunction with field-conducted tree-health surveys to test association between S. tsugae and tree health. S. tsugae were recovered from 13 of 65 sites (20%); recovery was significantly associated with older release sites which indicates that S. tsugae may require more time to reach readily detectable levels. Regression analysis indicated that establishment was positively associated with the average maximum temperature seven days following release and elevation. Several significant correlations were found between presence of S. tsugae, and year of release, season of release, and temperature variables. These results indicate that S. tsugae should be monitored for establishment for at least five years following releases to enhance knowledge of establishment. Coexistence of three predatory beetles, S. tsugae, L. nigrinus and L. rubidus, was observed on the same hemlock trees. Significant differences between normalized difference vegetation index values and S. tsugae presence was observed. For understory and overstory hemlock, percent crown transparency, percent live crown, and percent branch dieback was also significant with presence of S. tsugae. Coexistence of S. tsugae and L. nigrinus on eastern hemlock may provide prolonged feeding on HWA. Predictive models would assist land managers in selecting appropriate times and sites for future releases. Application of digital imagery could be used to evaluate other natural enemies in forest landscapes.
Hakeem, Abdul, "Assessment of Factors Affecting Establishment of Biological Control Agents of Hemlock Woolly Adelgid on Eastern Hemlock in the Great Smoky Mountains National Park. " PhD diss., University of Tennessee, 2013.