Date of Award


Document Type


Degree Name

Master of Science (MS)


Natural Resources

First Advisor

Kimberly Wallin

Second Advisor

Bill Keeton


Hemlock woolly adelgid (Adelges tsugae) is a non-native, invasive pest of eastern hemlock (Tsugae canadensis) and Carolina hemlock (Tsugae caroliniana), both of which are considered important foundation species in forest ecosystems. Adelges tsugae has caused widespread decline and mortality of hemlock trees in eastern North America. Native hemlocks are particularly vulnerable because of the absence of co-evolved plant defenses and lack of natural enemies of A. tsugae. Managing A. tsugae through development of a biological control program has great potential at the regional level. Two species of silver fly from the Pacific northwest (PNW) Leucotaraxis argenticollis and Leucotaraxis piniperda are being studied as potential biological control agents for this purpose, with individuals from wild populations being collected and examined for biological control effectiveness. However, a limitation has been the lack of efficient collection methods for Leucotaraxis spp. sufficient to yield adequate numbers for research and operational releases. In this study, Le. argenticollis and Le. piniperda were assessed for i) the quantitative impacts they have on A. tsugae ovisacs, and ii) the phenology of adult Leucotaraxis spp. in the PNW. Data on observed predation impacts were collected at two locations in North Carolina. Hemlock tree branches infested with A. tsugae were caged with mesh bags and Leucotaraxis spp. were released inside. A. tsugae ovisacs were counted before and after collections. The phenology of adult Leucotaraxis spp. in the PNW was characterized using a degree day model from five years of collection data. Our results show a Leucotaraxis spp. emergence window of 566-730 degree days which aligns with 126-145 Julian days in the study region. Significant negative effects on A. tsugae ovisac counts between controls and Leucotaraxis spp. treatments were found atfound 8 weeks after initial release. These results will help researchers and managers with more effective timing of collections in the PNW and controlled releases of Leucotaraxis spp. within the range of eastern hemlock species.



Number of Pages

90 p.