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Title: Biophysical characteristics of Adelges tsugae feeding sites on six hemlock (Tsuga) species and a hybrid: implications for resistance

item OTEN, K - North Carolina State University
item Bauchan, Gary
item FRAMPTON, F - North Carolina State University
item HAIN, F - North Carolina State University

Submitted to: Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2012
Publication Date: 11/15/2012
Citation: Oten, K., Bauchan, G.R., Frampton, F.P., Hain, F.P. 2012. Biophysical characteristics of Adelges tsugae feeding sites on six hemlock (Tsuga) species and a hybrid: implications for resistance. Journal of Botany. 90:1170-1178.

Interpretive Summary: The hemlock woolly adelgid is a major insect pest of hemlock trees. The insect feeds at the junction of the needle and the stem. We studied the junction surface morphology and internal anatomy of six hemlock species and a hybrid using scanning electron microscopy. We compared the 4 species and the hybrid which are resistant to the wooly adelgid with two native species, the Eastern and Carolina hemlock, which are susceptible and discovered that the cuticle thickness at the junction appeared to be thicker in the resistant species than in the susceptible species. Observations of the thickness of the junction cuticle may be used by researchers to determine resistance to the hemlock woodly adelgid in selecting for resistance.

Technical Abstract: Characteristics of the plant surface significantly affect host-plant selection by phytophagous insects. Surface morphology of six hemlock species (Tsuga spp.) and a hybrid was investigated using low-temperature scanning electron microscopy. Observations focused on trichome presence and placement and cuticle thickness. These characteristics were studied in the context of species-level host-plant resistance to the hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), an exotic insect causing massive mortality to eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana) in the eastern United States. Hemlocks in the native range of the insect do not succumb to infestations and the mechanism of resistance is unknown. We addressed the potential role of plant surface morphology in the adelgid-hemlock interaction by comparing four adelgid-resistant hemlock species and a hybrid with the two adelgid-susceptible hemlock species. We found trichomes are likely not involved in conferring resistance to A. tsugae. Cuticle thickness may be involved in insertion site selection by A. tsugae, and may therefore have implications for resistance. The cuticle is thinnest at the point of A. tsugae stylet insertion and thus may affect A. tsugae feeding.