Carla Dilling
Hemlock woolly adelgid, Adelges tsugae Annand, is an invasive species reducing populations of eastern hemlock, Tsuga canadensis (L.) Carrière, throughout the eastern United States. Systemic imidacloprid and horticultural oil are the primary chemicals used to suppress infestations of this invasive pest. The impact of imidacloprid and horticultural oil on non-target canopy insects is unknown. A study was initiated in November 2005 to assess the effects of imidacloprid soil drench, soil injection, and tree injection applications, and horticultural oil applications on multiple levels of organization within the phytophagous and transient insect community (composition, overall species richness and abundance, guild species richness and abundance, and individual species). Analysis of similarity (ANOSIM) of Bray-Curtis distances infer significant differences between community composition and treatments. Mean species richness and abundance were significantly reduced by one or more application methods. Species richness was significantly reduced among detritivore and phytophaga guilds by soil drench applications. Species abundance was significantly lower across all guilds with the exception of the haematophaga guild, and also differed significantly from those species on the control trees. From 293 species identified, 35 were found to be directly affected by one or more of the chemical treatments. Of these 35 species, 27 were lepidopterans that directly consume needles of eastern hemlock and pupate in the soil. The remaining eight species were psocopterans that feed on micro-fungi found on the needles. This research will provide land managers and owners information to use in making decisions on treatment methods with lower non-target impacts.
Keywords: EASTERN HEMLOCK, HEMLOCK WOOLLY ADELGID, IMIDACLOPRID, NONTARGET CANOPY INSECTS
