Arboriculture & Urban Forestry 38(2): March 2012 cm (2.81) likely limited refoliation. Residues increased in 2009 (3.14 µg/g) and adelgid density dropped and remained low; percent tip growth in 2010 showed signs of recovery. The observation of imidacloprid accumulation (in the injected hemlocks) over time may be explained by its slow upward move- ment from stem to foliage. It is conceivable that the imidacloprid is stored within the xylem axial and radial parenchyma (living symplast) in the tree, or that its slow upward movement is related to binding to cellulose (the non-living apoplast), particularly in the minute conifer tracheids. Xylem cellulose is 44% carbon (Heu- kelekian and Waksman 1925), constituting an extensive adsorp- tive surface. The carbon adsorption coefficient of imidacloprid is ~350, which suggests moderate adhesion in the xylem (Cox et al., 1977). Whatever the precise mechanism (symplast absorption or apoplast adsorption), systemic application of imidacloprid in an evergreen tree is retained and/or accumulates over the leaf’s lifes- pan. In Eastern hemlock needles are retained perennially (i.e., from three to six years) (Ford and Vose 2006). This observation has implications on extending the insecticide application interval. Forecast plots were conducted to predict imidacloprid residues in hemlock over time, which suggest sustained ac- tivity against HWA from a single treatment of imidaclo- prid for a period of four to six years. These data suggest that the low rates of tree injected imidacloprid could be admin- istered once every three to four years to protect woodland trees. High rate injection or the one-two strategy (of tree and soil injection) may afford longer (six years) term protection of hemlock. Early systemic activity and extended re-treatment cycles are attractive from both efficacy and economic stand- points, particularly if large numbers of trees require treatment. Acknowledgements. The authors gratefully acknowledge Royce Clay, Arborist for the Biltmore Estate for providing the annual samples needed to conduct the assays, and the support of Reed N. Royalty, Insecticide Product Development Manager, Bayer Environmental Science (Clayton, NC) for providing the Merit 75 WSP for the study and for supporting the imidacloprid residue analyses. The authors also thank Brenda I. Cruz for assistance in conducting the hemlock assessments. The authors thank Joe Fischer and Brian L. Strom, USFS Southern Research Station (Pineville, LA) for conducting the ELISA analyses, and to Cavell Brownie, Profes- sor Emeritus, North Carolina State University (Raleigh, NC) for conduct- ing the RM statistical analyses. LITERATURE CITED Chiriboga, C.A. 2009. Physiological responses of woody plants to imida- cloprid formulations. M.S. Thesis. Ohio State University. Columbus, Ohio, U.S. 146 pp. Cowles, R.S., M.E. Montgomery, and C.A.S-J. Cheah. 2006. Activity and residues of imidacloprid applied to soil and tree trunks to control hemlock woolly adelgid (Hemiptera: Adelgidae) in forests. Journal of Economic Entomology 99:1258–1267. Costa, S.D., M. Skinner, and B. L. Parker. 2004. HWA cold-hardiness: to- wards defining limits of range expansion. In: Proceedings, XV USDA Intragency Research Forum on Gypsy Moth and Other Invasive Spe- cies. GTR-NE-322. pp. 19–22. Cox, L., W.C. Koskinen and P.Y. Yen. 1997. Sorption-desorption of im- idacloprid and its metabolites in soils. Journal of Agricultural and Food Chemistry 45:1468–1472. Cregg, B.D., Mota-Sanchez, D. McCullough, R. Hollingworth, and T. Poland. 2005. Distribution and persistence of trunk-injected 14 C imi- 47 dacloprid in ash trees. In: Emerald Ash Borer Research and Technolo- gy Development Meeting. September 26–27, 2005. FHTET-2005-16. pp. 24–25. Cruziat, P., H. Cochard, and T. Ameglio. 2002. Hydraulic architecture of trees: Main concepts and results. Annals of Forestry Science 59:723–752. Dilling, C., P. Lambdin, J. Grant, and R. Rhea. 2010. Spatial and tem- poral distribution of imidacloprid in eastern hemlock in the southern Appalachians. Journal of Economic Entomology 103:368–373. Doccola, J., E. Bristol, S. Sifleet, J. Lojko, and P. Wild. 2007. Efficacy of trunk-injected imidacloprid in the management of hemlock woolly adelgid (Adelges tsugae). Arboriculture & Urban Forestry 33:12–21. Esau, K. 1977. The Anatomy of Seed Plants. Second Edition. John Wiley and Sons. New York, New York, U.S. 550 pp. EXTOXNET. Extension Toxicology Network. Pesticide Information Profiles. IMIDACLOPRID. Accessed 1/14/2010. Fischer, J., B. Strom, and S. Smith. 2009. Evaluation of a commercially available ELISA kit for quantifying residues in Erythrina sandwicen- sis leaves for management of the Erythrina gall wasp, Quadrastichus erythrinae Kim. Pan-Pac. Entomol. 85:99–103. Ford, C., and J. Vose. 2006. Eastern hemlock transpiration: Patterns, con- trols, and implications for its decline in southern Appalachian forests. In Second Interagency Conference on Research in the Watersheds. May 16–18, 2006. USDA ARS. Coweeta Hydrologic Laboratory. 8 pp. Havill, N. P., M.E. Montgomery, G. Yu, S. Shiyake, and A. Caccone. 2006. Mitochondrial DNA from hemlock woolly adelgid (Hemiptera: Adelgiddae) suggest cryptic separation and pinpoints the source of the introduction to eastern North America. Annals of Entomology Society of America 99:195–203. Heukelekian, H., and S.A. Waksman. 1925. Carbon and nitrogen trans- formations in the decomposition of cellulose by filamentous fungi. Journal of Biological Chemistry 66:323–342. Kramer, P.J., S.G. Pallardy, and T.T. Kozlowski. 1996. Physiology of Woody Plants. Second Edition. Academic Press. 411 pp. Lawson, A.B., and D.L. Dahlten. 2003. Evaluation of systemic insecti- cides as a treatment option in integrated pest management of the elm leaf beetle, Xanthogalleruca luteola (Müller) (Coleoptera: Chryso- melidae). Journal of Economic Entomology 96:1455–1462. Lehotay, S.J., K.A. Son, H. Kwon, U. Koesukwiwat, W. Fu, K. Mas- trovska, E. Hoh, and N. Leepipatpiboon. 2010. Comparison of QuEChERS sample preparation methods for the analysis of pesti- cide residues in fruits and vegetables. Journal of Chromatography A 1217:2548–2560. McClure, M.S. 1987. Biology and control of hemlock woolly adelgid. Bull. Conn. Agric. Exp. Stn. 851. McClure, M.S. 1991. Density-dependent feedback and population cycles in Adelges tsugae (Homoptera: Adelgidae) on Tsuga canadensis. En- vironmental Entomology 20:258–264. McClure, M.S. 1992. Effects of implanted and injected pesticides and fertilizers on the survival of Adelges tsugae (Homoptera: Adelgidae) and on the growth of Tsuga canadensis. Journal of Economic Ento- mology 85:468–472. Montfort, K.A., S.L. Reynolds, S.A. Thorpe, and S.N. White. 1994. Comparison of ELISA and HPLC techniques for the analysis of car- bendazim and thiabendazole residues in fruit and vegetables. Food and Agriculture Immunology 6:17–22. Montgomery, M.E., D. Yao, and H. Wang. 2000. Chinese Coccinellidae for biological control of the hemlock woolly adelgid: description of native habitat. Proceedings: Symposium in Sustainable Management of Hemlock Ecosystems in Eastern North America. GTR-NE-267. pp. 97–102. ©2012 International Society of Arboriculture
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