The shady, cool ecosystems that characterize hemlock stands are under threat by the hemlock woolly adelgid, Adelges tsugae Annand (HWA), in eastern North America. Eastern and Carolina Hemlock trees, Tsuga canadensis and T. caroliniana, are now considered “Near Threatened” on IUCN’s Red List of Threatened Species. Effective dispersal methods, toxic saliva, and a dearth of natural predators have made this invasion a harbinger of hemlock death. The loss of this keystone species has increased nitrification rates, stream temperatures, and soil pH. As species compositions favor more birch, oak, and maple, higher winter transpiration can lead to decreased soil moisture. This creates an escalated risk for disturbances such as invasive species encroachment and fire, driving alarming changes for the plants, animals, and humans that live in and around them.
Several insect predators from HWA’s native range show promise for biological control. Larvae of Leucopis piniperda and Leucopis argenticollis, silver flies from the Pacific Northwest (PNW), were found to be the most abundant predators in association with HWA. Their ability to target both the sistens and progrediens generations of HWA could make them a powerful predator in the fight to save the hemlocks in eastern North America.
Results/Conclusions
This study seeks to assess the merit of Leucopis spp. from the PNW as predators for HWA in eastern North America. As many questions remain on Leucopis spp.’s overwintering behavior, voltinism, phenology, and interactions with other predators, this study focuses on analyzing these four issues in three sites in Great Smoky Mountain National Park, The Cary Institute, and a site in Pennsylvania (TBD). Controlled releases have yielded data on the ability of Leucopis spp. to survive in east coast summer conditions. Initial results from a site at the Cary Institute from May 31st to July 12th, 2017, indicate altered voltinism between Leucopis spp. in the eastern United States, with the development of a F1 generation in just six weeks. Temperature data, using iButtons™, will be gathered for a full year, which will reveal winter survival rates and impacts of temperature on Leucopis spp. development. Full-tree enclosures will indicate whether Leucopis spp. may have spatial preferences on hemlock trees (ie favoring tree canopy versus understory). Finally, Leucopis spp. and Laricobius nigrinus will be co-released to observe any interactions between the two predators.