Emerald ash borer (Agrilus planipennis) larval development on blue ash (Fraxinus quadrangulata) and green ash (F. pennsylvanica): Field and laboratory experiments

Emerald ash borer (EAB) (Agrilus planipennis) is a primary pest that has killed tens of millions of North American ash (Fraxinus spp.) trees. Most ash trees that this pest has encountered have suffered high mortality rates in Eastern North America. However, blue ash (F. quadrangulata) is relatively resistant and appears to be able to survive EAB infestation. To explore the mechanism of resistance, I compared the capacity of EAB larvae to survive and develop on blue ash and the more susceptible green ash (F. pennsylvanica). Blue and green ash trees were infested in the field and laboratory with EAB eggs and later peeled to extract larvae and determine their developmental stages. In field and laboratory studies, larvae reared on both species of ash had the same rates survivorship.  In both species rates of larval mortality due encapsulation by wound periderm were low (<4%). Larvae on field grown blue ash were significantly smaller and there were fewer overwintering as J-shape (prepupae) than on green ash. Similarly, laboratory larvae reared on blue ash were significantly smaller over time than on green ash. Interestingly, J-shaped larvae on green and blue ash weighed the same. This suggests that EAB larvae develop more slowly in blue ash than in green ash and that a larger proportion have a semivoltine life cycle. These findings are consistent with another that shows EAB larvae to have slowed development in Asian ash species. Therefore, increased survival of blue ash observed in the North American forest may be explained by antibiosis that leads to a longer period of development during which larvae can be attacked in the tree by natural enemies.