HEMLOCK WOOLLY ADELGID (HOMOPTERA, ADELGIDAE) - STYLET BUNDLE INSERTION AND FEEDING SITES

Stylet bundle insertion site, path traveled, and feeding site were exa mined for the hemlock woolly adelgid, Adelges tsugae Annand, on needle s from current and previous years of eastern hemlock Tsuga canadensis Carriere. The stylet bundle is composed of 4 individual stylets-2 oute r mandibular stylets and 2 inner maxillary stylets. A. tsugae inserts its stylet bundle on the adaxial side of eastern hemlock needles, prox imal to the twig with respect to the leaf abscission layer. Insertions are primarily intracellular through epidermal cells. Once inserted, t he stylet bundle then follows a mixed intracellular and intercellular pathway, the latter predominating, when penetrating the plant tissue t o the feeding site, the xylem ray parenchyma cells. We observed eviden ce of salivary secretions, tracks, and sheaths produced by A. tsugae i n the plant similar to those produced by aphids and other adelgids in their host plants. Unlike other adelgids studied, which feed on cortic al parenchyma cells and on solutes from phloem of their spruce hosts, A. tsugae appears to feed only on storage cells, the parenchyma cells which comprise the xylem rays. This suggests that the intense effect o f A. tsugae on eastern hemlock may be caused by factors other than its food consumption, that is, a possible toxin effect, or altered host p lant response to environmental conditions.