8 Weston and Harper: Potential of Tsuga spp. to Replace Eastern Hemlock 2004; Havill and Montgomery 2008). The form of T. chinensis is also quite similar to T. canadensis , although the branches of T. chinensis tend to “weep” more than those of T. canadensis , and the needles are larger, generally darker and more lustrous, and more sparsely arrayed on the branches (pers. obs.) ( Figure 3 ). It remains to be seen how large of a geographic area in the United States possesses a suitable climate for growth of T. chinensis. The species is more closely related to T. caroliniana than to T. canadensis (a more northerly species) based on results of breeding experiments (Bentz et al. 2002), yet still apparently thrived in the Hudson Valley of New York State, suggesting that it might be more broadly adapted to the climate in the United States. Acknowledgments. Funding for establishment of the trees and initial data collection came from the NYS Integrated Pest Management pro- gram, and funding for continued data collection came from the U.S. Forest Service. Assistance for data collection over the duration of the project was provided by Jerry Giordano, Lora Schwartzberg, Betsy Lamb, and Gaylord Desurmont. Special thanks go to Ted Kozlowski, his crew, and the Westchester County Parks for providing space at Lasdon Park and Arboretum for the plots and access to equipment and mulch for maintaining the plots. LITERATURE CITED Bentz, S.E., L.G.H. Riedel, M.R. Pooler, and A.M. Townsend. 2002. Hybridization and self-compatibility in controlled pollinations of eastern North American and Asian hemlock ( Tsuga ) species. Journal of Arboriculture 28:200–205. Figure 3. Photograph of Tsuga chinensis . (χ 2 = 8.92, P = 0.0028). There was no association between the two insects on the other test species. Overall arthropod abundance on the test trees was low; most trees had none present at any of the sampling times. The most fre- quently encountered arthropods were spiders ( n = 121), earwigs ( n = 34), fungus gnats ( n = 15), and robber flies ( n = 11). Of these, only spiders would be expected to possibly feed on adel- gids (although robber flies are predaceous, they prey on flying insects). Regression analysis revealed that spiders (or their webs) were most common on T. chinensis ; significantly fewer were found on T. canadensis , and still fewer were found on the remain- ing species, which were not statistically different from each other (overall ANOVA F = 9.78; P < 0.0001; df = 6, 128). It seems that tree size may have been more important than prey in determining the abundance of spiders because T. canadensis and T. chinensis were by far the largest trees. Other factors likely influence spi- der abundance, however, because their abundance was higher on T. chinensis despite that fact that these trees were considerably smaller than T. canadensis ( Table 2 ). The presence of spiders on T. chinensis does not likely explain the absence of adelgids on this species because spiders are not known to prey on adelgids (Wallace and Hain 2002). The results point strongly toward T. chenensis as a possible replacement for T. canadensis in the northeastern United States, if not beyond. Tsuga chinensis was most similar in our study to T. canadensis in terms of growth and vigor and appeared to be vir- tually immune to hemlock woolly adelgid based on our findings and those of others (Bentz et al. 2002; Del Tredici and Kitajima ©2009 International Society of Arboriculture Del Tredici, P., and A. Kitajima. 2004. Introduction and cultivation of Chinese hemock ( Tsuga chinensis ) and its resistance to hemlock woolly adelgid ( Adelges tsugae ). Journal of Arboriculture 30:282–287. Gouger, R.J. 1971. Control of Adelges tsugae on hemlock in Pennsyl- vania. Scientific Tree Topics 3:1–9. Havill, N.P., and M.E. Montgomery. 2008. The role of arboreta in study- ing the evolution of host resistance to the hemlock woolly adelgid. Arnoldia 65:2–9. McClure, M.S. 1991. Nitrogen fertilization of hemlock increases suscepti- bility to hemlock woolly adelgid. Journal of Arboriculture 17:227–229. ———. 1992. Hemlock woolly adelgid. American Nurseryman 175:82–89. Rose, M.A., and E. Smith. 1996. Fertilizing Landscape Plants. Ohio State University Factsheet HYG 1002-96. Wallace, M.S., and F.P. Hain. 2002. Summary of native and estab- lished predators of the hemlock woolly adelgid and the balsam woolly adelgid (Homoptera: Adelgidae) in the southeastern United States, pp. 141–149. In: Onken, B., R. Reardon, and J. Lashomb (Eds.). Proceedings, Symposium: Hemlock Woolly Adelgid in the Eastern U.S., 5–7 February, 2002, East Brunswick, NJ. USDA Forest Service. Ward, J.S., M.E. Montgomery, C.A.S.-J. Cheah, B. Onken, and R.S. Cowles. 2004. Eastern Hemlock Forests: Guidelines to Minimize the Impacts of Hemlock Woolly Agelgid. USDA Forest Service, Morgantown, WV. Paul A. Weston (corresponding author) Department of Entomology Cornell University Ithaca, NY 14853, U.S.
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[email protected] Richard W. Harper Cornell Cooperative Extension of Westchester County Valhalla, NY 10595, U.S.
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