Arboriculture & Urban Forestry 46(5): September 2020 Arboriculture & Urban Forestry 2020. 46(5):347–357 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Another Look at Systemic Neonicotinoid Applications for Emerald Ash Borer Suppression By David G. Olson, Lee H. Townsend, Eric Roemmele, and Lynne K. Rieske Abstract. Emerald ash borer (EAB, Agrilus planipennis) is an invasive phloem feeder from East Asia that has killed millions of ash trees in North America. Currently, effective options for individual tree protection are limited to systemic insecticides, in particular neonicotinoids, which have come under increased scrutiny for their nontarget effects. In this study, green ash (Fraxinus pennsylvanica) trees were treated with two neonicotinoid insecticides, imidacloprid and dinotefuran, at full and half label rates based on trunk diameter to evaluate residues and effi- cacy. Analyzing the leaf, stem, and root tissues, there was no difference in insecticide residues between application rates within each tissue type. However, there were significantly higher residues of imidacloprid in root tissue compared to other plant tissues, and dinotefuran applied at the full label rate resulted in lower residues in stem phloem tissue. Additionally, insecticide-treated stems were artificially infested with EAB eggs to measure larval success (survival and growth). EAB larvae consumed less phloem in treated trees compared to untreated controls. These find- ings suggest that, in small-diameter ash, lower than label-recommended doses may be a viable component of an integrated management plan for EAB. Keywords. Agrilus planipennis; Dinotefuran; Fraxinus; Imidacloprid. 347 INTRODUCTION Emerald ash borer (EAB, Agrilus planipennis Cole- optera: Buprestidae), an invasive pest of forest, shade, and ornamental ash (Fraxinus spp.), has caused exten- sive tree mortality throughout its invaded range in North America (USDA APHIS 2020) and is expected to have caused $10 billion in losses by the year 2019 (Kovacs et al. 2011). EAB has a one- or two-year life cycle, depending on latitude (Herms and McCullough 2014). In sum- mer, adults mate and each female oviposits about 70 eggs on stems and large branches of ash hosts (Rut- ledge and Keena 2012). Eggs hatch and larvae feed on phloem, creating serpentine galleries beneath the bark (Figure 1a). Mature larvae overwinter before pupating and emerging as adults the following or sub- sequent summer (Cappaert et al. 2005). When beetle populations are high, larval feeding girdles trees and causes rapid tree mortality (Herms and McCullough 2014)(Figure 1b). All North American ash are susceptible to EAB colonization (Liu et al. 2007), though white and green ash (F. americana and F. pennsylvanica) are highly preferred, and blue ash (F. quadrangulata) has some putative resistance (Tanis and McCullough 2012; Spei and Kashian 2017). In the eastern US, ash trees are a significant component of wildland forests (Wharton and Barbour 1973) and are also prevalent as street, park, and landscape trees. Because of its pervasiveness, efforts at EAB management in the USA have focused on classical biological control (Duan et al. 2012; Duan et al. 2013). Four hymenopteran parasitoids, Spathius agrili (Braconidae), S. galinae (Braconidae), Tetrastichus planipennisi (Eulophidae), and Oobius agrili (Encyrtidae), discovered in EAB’s native range of China, have been intensively screened and are now laboratory reared in the USA for incor- poration into biological control releases throughout the invaded range. Additionally, endemic natural ene- mies have been recruited to EAB-invaded forests and may be helping to suppress EAB populations (Duan et al. 2013; Davidson and Rieske 2016; Savage and Rieske 2018). Classical biological control has had some success suppressing EAB populations (Duan et al. 2011) and has also been deployed in concert with chemical ©2020 International Society of Arboriculture
September 2020
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