108 also others having only Asian parentage (e.g., ‘New Horizon’, ‘Morton Glossy Triumph’). This data supports U. americana, U. parvifolia, and U. propinqua as relatively resistant to K. ulmi. Agromyza aristata, the only North American dipteran leaf miner commonly associated with Ulmus spp. (Spencer 1973), was the most abundant leaf miner at the study site in 2006. It was found mainly on U. americana. It was decimated by extensive freeze damage to young leaves in April 2007 and its numbers re- mained relatively low through 2008 and 2009. Except for a brief biological synopsis (Needham et al. 1928), the authors’ literature search found no previous published research on its life history. EEFW is native to England and much of continental Europe (Pitkin et al. 2008). It was first reported in the Midwestern United States in 2003; by 2006, when this study was initiated, the Euro- pean elm flea weevil had been documented only from Illinois and Wisconsin (Anderson et al. 2007). Findings from the present study are a new state record for Kentucky. Where and in what life stage EEFW overwinters was not confirmed. Anderson et al. (2007) speculated that adults overwinter on or near the host tree, noting their appearance on elm trees in the early spring, as the buds are be- ginning to expand. Those observations are consistent with current findings of numerous weevils mating and laying eggs in expanding leaves by early April. By 2009, EEFW had become so abundant on some elm cultivars that the brown, vacated mines and adult feeding holes compromised the aesthetic quality of the trees. Moreover, the European elm flea weevil damaged all species and cultivars of elms, albeit some more than others. An Internet search (August 11, 2009) yielded postings about EEFW outbreaks in Illinois, Wiscon- sin, Michigan, Ohio, Colorado, and other states, with particularly heavy damage on Siberian elm, U. pumila, and on the hybrid cultivar ‘Homestead’. EEFW is destructive enough to be a pest of concern for production nurseries and could rival Japanese beetle in com- promising the aesthetics of otherwise suitable elms in landscapes. In summary, although none of the elms in the National Elm Trial is resistant to all insect pests, based on available data they do differ in susceptibility to particular pest species. U. parvifo- lia, U. propiqua, and most of the hybrid cultivars are resistant to A. aristata, whereas American elms as a group are susceptible to that leaf miner. In contrast, some hybrid cultivars (e.g., ‘New Horizon’) are highly susceptible to both K. ulmi and aphid pouch galls, which are absent or nearly absent on U. americana, parvifo- lia, and propinqua, whereas others (e.g., Frontier) are resistant to those pests. The two most destructive pests, Japanese beetle and EEFW, had the broadest host range. Most American elms showed some relative resistance to both, but ‘Jefferson’, which was high- ly resistant to EEFW, is susceptible to Japanese beetle damage. Notably, most of the hybrid cultivars, including the otherwise pest- and disease-resistant U. parvifolia cultivars, are suscep- tible to EEFW, an invasive pest that seems to be expanding its geographical range in the United States. Of the hybrids, ‘Mor- ton Accolade’ was relatively resistant to EEFW whereas ‘Home- stead’ was very heavily damaged by EEFW larvae and adults. Awareness of such differences in resistance may help home- owners, landscapers, and urban foresters to select and plant elm trees that will simplify future pest management requirements. For example, U. parvifolia and U. propiqua would be good choices for areas where Japanese beetles are abundant, but might require periodic treatment for EEFW. Planting ‘Jefferson’ elms would like- ly limit the impact of EEFW, but managers would need to be pre- pared to implement Japanese beetle suppression. Development and ©2010 International Society of Arboriculture Condra et al.: Elm Resistance to Insect Pests release of Dutch elm disease-resistant Ulmus spp. has considerable promise for diversifying urban and suburban landscapes threatened by potentially lethal invasive insects and pathogens. Resistance to other native and exotic pests, such as the ones discussed herein, should also be a consideration for selecting the best-adapted and sustainable landscape trees for particular geographical regions. Acknowledgments. We are grateful to J. Hartman and E. Dixon for planting and maintaining the University of Kentucky (UK) National Elm Trial plot and allowing us access to the trees. R.S. Anderson (Canadian Museum of Nature, Ottawa) and S.E. Halbert (Florida State Collection of Arthropods, Gainesville) kindly identified voucher specimens of Eu- ropean elm flea weevil and gall aphids, respectively. We thank C. Elder, J. George, V. Jacquier, B. Potter, and C. Redmond for help with data collection, R. Bessin who took some of the photos (Figures 1b, 1c; and Figures 2a, 2b), and J. Boggs (The Ohio State University) and J. Hartman (UK) for critically reading the manuscript. A grant from the UK Nursery Research Endowment partially supported this work. This is paper 09- 08-082 of the Kentucky Agricultural Experiment Station. The first and second authors contributed equally to this work. LITERATURE CITED Analytical Software. 2008. Statistix version 9.0; User’s manual. Analyti- cal Software, Tallahassee, FL. Anderson, R.S., C.W. Obrien, G.A. Salsbury, and S.J. Krauth. 2007. Orchestes alni (L.) newly discovered in North America (Coleoptera: Curculionidae). Journal of Kansas Entomological Society 80:78–79. Blackman R.L., and V.F. Eastop. 1994. Aphids on the world’s trees. CAB International. Wallingford, UK. Bosu, P.P., F. Miller, and M.R. Wagner. 2007. Susceptibility of 32 elm species and hybrids (Ulmus spp.) to the elm leaf beetle (Coleoptera: Chrysomelidae) under field conditions in Arizona. Journal of Eco- nomic Entomology 100:1808–1814. Brasier, C.M., and M.D. Mehrotra. 1995. Ophiostoma himal-ulmi sp. Nov., a new species of Dutch elm disease fungus endemic to the Himalayas. Mycological Research 99:205–215. Guries, R.P., and E.B. Smalley. 1994. Variation in elm leafminer inju- ry on elms in Wisconsin, pp. 62–78. In: Proc. 8th METRIA Conf., Metropolitan Tree Improvement Alliance, U.S. National Arboretum, Washington, D.C. Hubbes, M. 1999. The American elm and Dutch elm disease. Forestry Chronicle 75:265–273. Jacobi, W., J. Klett, and J. Walla. 2009. National Elm Trial overview. . Johnson, W.T., and H.H. Lyon. 1988. Insects that feed on trees and shrubs, 2nd Edition. Cornell Univ. Press, Ithaca, NY. Ladd, T.L., Jr. 1987. Japanese beetle (Coleoptera: Scarabaeidae): Influ- ence of favored food plants on feeding response. Journal of Economic Entomology 80:1014−1017. Loughrin, J.H., D.A. Potter, T.R. Hamilton Kemp, and M.E. Byers. 1996. Role of feeding-induced plant volatiles in aggregative behavior of the Japanese beetle (Coleoptera: Scarabaeidae). Environmental Entomol- ogy 25:1188−1191. Merkle, S.A., G.M. Andrade, C.J. Nairn, W.A. Powell, and C.A. May- nard. 2007. Restoration of threatened species: a noble cause for trans- genic trees. Tree Genetics & Genomes 3:111–118. Miller, F. 2000. Insect resistance of elm genotypes, pp. 137–154. In: C.P. Dunn (Ed.). The elms: Breeding, conservation, and disease manage- ment. Kluwer, Boston.
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