In its native range within Asia, hemlock woolly adelgid (HWA), Adelges tsugae, is not a very serious or destructive pest. Populations levels are controlled by natural enemies and by host resistance. The HWA was first reported in western Canada (British Columbia), in the 1920's and in the United States (Virginia), in the 1950's. In the eastern US, all sizes and ages of eastern hemlock, Tsuga canadensis, and Carolina hemlock, T. caroliniana, are susceptible to HWA infestations. In British Columbia, damage to western hemlock, T. heterophylla, has been minor.