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.