Emerald Ash Borer

Scientific name: Agrilus planipennis

Native Range: East Asia

At Risk

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.

Distribution

Emerald ash borer is native to East Asia and was discovered in Detroit, Michigan and Windsor, Ontario in 2002. Indications are that it may have been introduced to this area as early as 1990 by means of infested wood packing material from Asia. Emerald ash borer has spread rapidly across the eastern United States due to the long distance movement of infested ash firewood, nursery stock and other ash materials. On May 14, 2009, EAB was discovered in the South Saint Anthony Park neighborhood in St. Paul, MN. Emerald ash borer is serious invasive tree pest, and consequently a quarantine has been placed to help slow the spread of EAB to other areas. For information on EAB distribution and quarantine boundaries, refer to the MDA's EAB status map.

Biology

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.

Identification

Emerald ash borer adults are small, metallic green wood boring beetles. They are about 3/8 - 1/2 inch long and 1/8 inch wide, which will fit on a penny. Emerald ash borer larvae are cream-colored, with bell shaped body segments. The larvae have two spine like projections at the end of their body called urogomphi that are a defining characteristic. Full grown larvae will reach about 1.5 inches long. Their size varies as they feed and grow underneath the ash tree's bark. The larvae create serpentine or "S" shaped galleries underneath the bark that are a definitive sign of EAB when found in ash trees. Emerald ash borer eggs and pupae are not commonly seen and are difficult to identify.

EAB "S" shaped larval tunneling — Emerald Ash Borer "S" shaped larval tunneling

Picture of EAB larva — Emerald ash borer larva

Picture of EAB adult beetle on quarter — Emerald ash borer adult beetle

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.

Regulatory Status: Regulated

Emerald ash borer is regulated at the state level. All ash material and hardwood firewood is prohibited from entering Minnesota from other states without proper certification. Refer to MDA's EAB Status Map for state quarantine boundaries.

Learn More

Insect Pests & Diseases Index

EAB Biological Control in Minnesota