||The eastern hemlock is a coniferous tree native to the eastern part of North America that forms an important ecological niche. Eastern Hemlocks are in danger of elimination due to infestation of a foreign pest known as the hemlock woolly adelgid (HWA). HWA remove vital nutrients from hemlock trees causing branch dieback and the eventual mortality of the tree. The U.S. Department of Agriculture, U.S. Forest Service has been treating the hemlock trees with a pesticide imidacloprid, [1-(6-chloro-3-pyridylmethyl)-2-nitroimino-imidazolidine], which has high insecticidal activity against the HWA. This thesis describes the development of an extraction method for imidacloprid from needle foliage and an LC/MS/MS method to detect and quantify the concentrations of imidacloprid and its metabolites in needle extracts supplied by the U.S. Forest Service. The method will be used to determine the amount of imidacloprid and its metabolites found in treated hemlock trees and to measure the uptake, persistence and mobility of these compounds as a function of the sample variables (needle age, application technique, growth year, and tree height and branch direction). Results indicate that the major compounds in hemlock needles are the imidacloprid and the olefin, dihydroxy and 6-chloronicotinic acid metabolites formed by oxidative pathways in hemlock trees. The olefin metabolite was stable in the tree and samples that were up to 8 years post-treatment still showed the presence of this metabolite while imidacloprid levels steadily decreased over time. Imidacloprid was evenly distributed throughout the height of the tree and cardinal direction of the branches. Both trunk injections and soil injections resulted in even distribution throughout the tree; however, a more rapid uptake was observed in the trunk injections.