Terrestrial Salamander and Ant Community Responses to Imidacloprid Application in Central Appalachian Eastern Hemlock Forests

Imidacloprid is the most widely used insecticide in the world and has been found to impact non-target taxa in systems in which it is applied. It is used as the primary treatment method in the protection of eastern hemlocks (Tsuga canadensis) from impacts of hemlock woolly adelgid (HWA; Adelges tsugae), an invasive insect in the U.S. that is causing widespread mortality of hemlock trees. In this study, we investigated whether imidacloprid applied in eastern hemlock forests is impacting woodland salamander and ant communities. In Chapter 1, I provide an overview of the ecological importance of eastern hemlocks and the HWA invasion, with a focus on invasion and management responses in the West Virginia National Park system. I then discuss biological and ecological aspects of the pesticide imidacloprid the ecological importance of eastern hemlocks, followed by a review of potential impacts of imidacloprid on amphibians and ants. Finally, I introduce the study area, discuss research needs, and define the objectives of the thesis research. In Chapter 2, we investigated whether imidacloprid applications were associated with woodland salamander abundance and health. We sampled terrestrial salamander communities at 18 control and treatment sites, respectively, with 12–17 surveys completed at each site. We tested the influence of three imidacloprid predictors on relative abundance and body condition while accounting for influential habitat characteristics. We did not find evidence for an overall difference in relative abundance between control and treatment plots. The body condition index score of adult salamanders was negatively associated with treated tree diameter at breast height (DBH), a proxy for treatment intensity, and positively associated with years since treatment (YST) at treatment sites. Furthermore, the YST relationship was stronger at sites with greater treated tree DBH. In addition, 8 eastern red-backed salamanders (Plethodon cinereus) collected from treatment areas contained imidacloprid, indicating terrestrial salamanders are uptaking the pesticide. In Chapter 3, we investigated the influence of imidacloprid treatments in eastern hemlock forests on ant relative abundance and diversity. Using bait traps, we sampled ants at 18 control and treatment sites, respectively, in spring, summer, and fall in 2020. We captured a total of 5 species and 17,626 ants, with 10,324 ants captured in control plots and 7,302 ants captured in treatment plots. We found that relative abundance of the dominant ant species (Aphaenogaster picea) exhibited a strong negative response to imidacloprid treatments. Recovery time of the species over time was dependent on treated tree DBH and years since the plot was treated, with abundances improving faster in sites with a lower amount of treated tree DBH. We found that ant diversity was also negatively impacted by imidacloprid treatments, but the effect was weaker, with coefficient confidence intervals overlapping 0. In addition, we detected imidacloprid in the biomass of ants collected from treatment sites, indicating ants are uptaking the pesticide. Overall, our study indicates that woodland salamanders and ants in eastern hemlock forests are negatively impacted by imidacloprid treatments, but they seem to recover over time. Salamanders and ants heavily influence the ecology of forest systems in the eastern U.S. They serve as important predators and prey and can have direct and indirect influences on the biological, physical, and chemical properties of soil and vegetation. The results of this thesis may help resource managers make informed decisions to balance the need for maintaining healthy eastern hemlock forests while minimizing impacts to non-target species