SEM images of western and eastern populations of hemlock woolly adelgid (Adelges tsugae)

The hemlock woolly adelgid (Adelges tsugae Annand) is an invasive pest that causes severe mortality in eastern hemlock (Tsuga canadensis Carriére) in eastern North America. The unchecked devastation is likely because of limited host resistance and the absence of natural enemies. Native to Japan and China, the adelgid also feeds on hemlock trees in western North America (western hemlock, Tsuga heterophylla Sargent, and mountain hemlock, Tsuga mertensiana (Bong.) Carriére), although it does not kill western hemlock populations owing to a combination of host resistance and native natural enemies. Genetic examinations revealed that the two adelgid populations are likely derived from different lineages; morphological and biological studies between the populations have not been investigated. The purpose of this study is to examine the morphology of the eastern population of the adelgid using scanning electron microscopy, to closely examine the feeding sites and apparatus, and to compare them to the western population of the hemlock woolly adelgid.