Tree vigor and its relation to emerald ash borer (Agrilus planipennis Fairmaire) larval development on green and white ash trees

Emerald ash borer (Agrilus planipennis Fairmaire, Coleoptera:Buprestidae) is an invasive pest of ash trees (Fraxinus spp.) in the USA and Canada. Density, mortality, and development of A. planipennis larvae were compared in 40 green ash (Fraxinus pennsylvanica) and 40 white ash (Fraxinus americana) trees, average 5.53 ± 0.09 cm diam. Trees were established in blocks in East Lansing, MI in 2007 and randomly assigned to four treatments: fertilizer, fertilizer + Agri-Fos® fungicide, girdled, or untreated (5 trees per species*treatment combination). Wild A. planipennis colonized these trees in 2008 and 2009. Foliage was periodically analyzed for nutrients, volatile production, and photosynthetic rate. In autumn 2008, 20 trees were felled and debarked to assess larvae. Foliage from girdled trees had significantly lower amino acids, protein:carbohydrate ratios, and photosynthetic rates than foliage from differently treated trees. Green ash larval density was significantly higher than white ash larval density in fertilizer and fertilizer + Agri-Fos trees. In green ash, larval density and mortality was significantly higher on girdled trees than on untreated and fertilizer + Agri-Fos trees. In white ash, larval density was significantly higher on girdled trees than on differently treated trees. Significantly more larvae developed in one year on girdled white ash than on white ash treated with fertilizer + Agri-Fos, where more larvae required two years of development. Fertilizer + Agri-Fos may slow larval development on white ash. Understanding variables that influence larval density, mortality, and development may help establish resistant ash cultivars and provide further control options for A. planipennis.