Emerald ash borer (EAB) kills ash trees. All ash trees (Fraxinus spp.) are susceptible to EAB. Millions of ash trees have already been killed across the midwest, eastern United States, and Canada. Minnesota has the highest volume of ash trees in the U.S. with nearly a billion forestland and urban ash trees combined. The potential for economic and environmental impacts of losing these trees is significant.
Emerald ash borer are small, iridescent green beetles that live outside of trees during the summer months. The larvae is worm-like and live underneath the bark of ash trees. Trees are killed by the tunneling of the larvae under the tree's bark. For a better understanding of the EAB life cycle, watch the video Cycle of Destruction.
In Minnesota, EAB completes one generation every one or two years. Eggs are laid from mid-June through August. Female EAB deposit their eggs individually on ash trees between layers of outer bark in cracks and crevices of the branches and trunk of the tree. The eggs typically hatch within two weeks, depending on temperature.
Emerald ash borer flight season begins May 1st
Minnesota Department of Agriculture considers May 1st - September 30th to be the flight season for EAB. This means that EAB adult beetles are emerging from infested trees or wood and flying in search of new hosts during this time. Emerald ash borer larvae complete their development by pupating into adult beetles in the spring and early summer. However, this process only occurs when temperatures are sufficiently warm and requires a certain amount of accumulated heat - i.e., development time. Accumulated heat can be measured and tracked using degree day models, which measures time spent above a specific temperature threshold.
For EAB, a base temperature of 50º F is used. The following are estimated thresholds of EAB development and activity:
450 degree days = First EAB adults begin to emerge
900-1100 degree days = Peak EAB adult activity
Current base 50º F degree day accumulations for Minnesota are available from the US degree-day mapping calculator.
Insects Commonly Confused with EAB
There are many insects in Minnesota that can be mistaken for EAB due to their size, shape or metallic green color. Identification can be difficult if the insect is not found associated with its ash tree host. For more information, refer to the Insects Commonly Confused with EAB reference sheet.