Arboriculture & Urban Forestry 36(3): May 2010 Arboriculture & Urban Forestry 2010. 36(3): 101–109 101 Resistance of Landscape-Suitable Elms to Japanese Beetle, Gall Aphids, and Leaf Miners, with Notes on Life History of Orchestes alni and Agromyza aristata in Kentucky Jennie M. Condra, Cristina M. Brady, and Daniel A. Potter Abstract. Twenty genotypes of landscape-suitable Dutch elm disease-resistant elms (Ulmus spp.) were evaluated in a replicated field study for resistance to multiple insect pests in Lexington, Kentucky, U.S. The European elm flea weevil (EEFW), Orchestes alni, a recently-introduced pest that disfigures elms by leaf-mining and adult feeding, was found as a new state record so its feeding preferences and life history were monitored. U. parvifolia and U. pro- pinqua, originally from Japan, were relatively resistant to Japanese beetles, and U. americana was generally less susceptible than most hybrids. Agromyza aristata, a serpentine leaf-mining fly, favored American elms, whereas Kaliofenusa ulmi a blotch-mining sawfly, and aphid (Tetraneura nigriabdominalis) pouch galls were uncommon on American and Asian elms but abundant on certain hybrids. EEFW infested all elms but at highest densities, (>20 mines per 30 cm shoot and >85 adult feeding holes per leaf), on certain hybrids. American elms, especially ‘Jefferson’, were somewhat less susceptible. EEFW laid eggs in expanding leaves; mines were initiated in late April and completed by mid- to late- May. Newly-emerged adults extensively damaged leaves in late May and June but nearly disappeared from tree canopies by mid-July. Implications for re-introduction of elms into urban landscapes are discussed. Key Words. Agromyza aristata; Dutch Elm Disease; Integrated Pest Management; Kalifenusa ulni; National Elm Trial; Orchestes alni; Tetraneura nigriabdominalis; Ulmus spp. Elms (Ulmus spp.), particularly the stately American elm (Ulmus americana), were once the dominant street and shade trees in cities and towns throughout North America (Hubbes 1999). Dutch elm disease (DED), which had already devastated elms in Europe, was first discovered in the United States in 1930 and quickly spread throughout eastern North America from several infection centers (Stipes and Campana 1981; Hubbes 1999). DED is caused by the wilt fungus Ophiostoma ulmi and is vectored by two species of elm bark beetles (Scolytidae). By 1977, pandemics of DED had killed approximately 56% of the original elm population in the eastern United States, roughly 43 million trees, causing great economic and aesthetic loss (Hubbes 1999; Merkle et al. 2007). Selection and breeding efforts to develop hardy DED-resistant American and hybrid elms have been underway for more than 70 years (Smalley and Guries 1993; Merkle et al. 2007). Although straight selection by inoculation screening has resulted in several DED-resistant pure American elm cultivars that were released to nurseries (Merkle et al. 2007), all North American elm spe- cies are susceptible (Hubbes 1999). Thus, the main sources for DED resistance genes are Asian elm species; e.g., U. parvifolia, U. pumila, U. propinqua, U. japonica, U. wilsoniana, and oth- ers (Smalley and Guries 1993; Hubbes 1999). DED fungus likely originated in the Himalayas (Brasier and Mehrotra 1995); thus, Asian elms may have had longer evolutionary time to develop resistance. A number of DED-resistant hybrid elms have been de- veloped from genetic combinations of Asian and, to lesser extent, European gene pools (Smalley and Guries 1993). Their growth habit, leaf size, and hardiness vary across different regions, how- ever, so does their resistance to pests other than Dutch elm dis- ease (Smalley and Guries 1993; Miller 2000; Bosu et al. 2007). Increasing pressure on shade trees from exotic pests such as emerald ash borer (Agrilus planipennis), Asian longhorned beetle (Anoplophora glabripennis), hemlock woolly adelgid (Adelges tsugae), and the sudden oak death/decline fungus (Phytopthora ramorum), as well as native pests such as bacterial leaf scorch (Xylella fastidiosa) underscores the importance of diversifying urban forests (Raupp et al. 2006). There is renewed interest in returning DED-resistant American and hybrid elms to streets and landscapes. To reduce the need for pesticide usage, how- ever, trees ideally should also be resistant to other pest species. The National Elm Trial is a cooperative effort to evalu- ate DED-resistant, commercially available American and hy- brid elms for horticultural characteristics and suitability for use across a range of environmental conditions in the United States (Jacobi et al. 2009). Large, replicated field trials were planted in 15 states, including Kentucky, providing the op- portunity for evaluating elms of differing parentage for sus- ceptibility to multiple insect pests. The authors report here on the relative resistance of 20 species and cultivars of DED- resistant, landscape-suitable elms to three species of leaf min- ers, pouch gall aphids, and Japanese beetles (Popillia japonica). One of the leaf miners found at the current study site was the European elm flea weevil (EEFW), Orchestes alni (Figure 1; Figure 2), an invasive pest first reported in the United States ©2010 International Society of Arboriculture
May 2010
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