Host Resistance of Five Fraxinus Species to Agrilus planipennis (Coleoptera: Buprestidae) and Effects of Paclobutrazol and Fertilization.

Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) has killed millions of Fraxinus spp. trees in North America. While all Fraxinus species assessed to date can be colonized, A. planipennis attraction to host trees varies among species and with tree health. We established a plantation of 105 trees (21 trees each of four North American species Fraxinus americana L., Fraxinus nigra Marshall, Fraxinus pennsylvanica Marshall, Fraxinus quadrangulata Michaux, and the Asian species, Fraxinus mandshurica Ruprecht), and determined whether resistance to A. planipennis could be enhanced by fertilizer or paclobutrazol applications. Differences among species overshadowed most treatment effects. In 2010, A. planipennis survival over 14 d was 53% when beetles were caged with F. nigra, 30-32% when beetles were caged with F. americana, F. pennsylvanica, or F. mandshurica, and only 14% for beetles caged with F. quadrangulata. In 2011, beetle survival was lower for beetles caged with F. quadrangulata (33%) than F. americana (72%) or F. mandshurica (80%). In 2010 and 2011, leaf weight consumed by beetles was the same among Fraxinus species. However, beetles caged on F. quadrangulata consumed less leaf area than that by beetles caged with other ash species. In 2011, when trees were exposed to wild A. planipennis, larval density (per m(2)) was highest on F. nigra (235.9 ± 36.41) and F. pennsylvanica (220.1 ± 39.77), intermediate on F. americana (40.7 ± 11.61), and lowest on F. quadrangulata and F. mandshurica (2.0 ± 0.98 and 1.5 ± 0.67, respectively). Results indicate F. quadrangulata and F. mandshurica were relatively resistant to A. planipennis, F. nigra and F. pennsylvanica were highly vulnerable, and F. americana was intermediate.

Spatial and temporal distribution of trunk-injected (14) C-imidacloprid in Fraxinus trees.

BACKGROUND: Since the discovery of Agrilus planipennis Fairmaire (emerald ash borer) in 2002, researchers have tested several methods of chemical control. Soil drench or trunk injection products containing imidacloprid are commonly used to control adults. However, efficacy can be highly variable and may be due to uneven translocation of systemic insecticides. The purpose of this study was to determine whether sectored xylem anatomy might influence imidacloprid distribution in tree crowns. RESULTS: Imidacloprid equivalent concentrations were higher in leaves from branches in the plane of the injection point (0°) than in leaves from branches on the opposite side of the injection point (180°). Leaves from branches 90° to the right of injection points had higher imidacloprid equivalent concentrations than leaves from branches 90° to the left of injection points. Leaves and shoots had higher imidacloprid equivalent concentrations than roots and trunk cores, indicating that imidacloprid moves primarily through the xylem. CONCLUSION: Imidacloprid equivalent concentration in leaves varied over time and in relation to injection points. It is concluded that ash trees have sectored 'zigzag' xylem architecture patterns consistent with sectored flow distribution. This could lead to variable distribution of imidacloprid in tree crowns and therefore to variable control of A. planipennis.