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Learn About Invasive Species

HOMEbreadcrumb separatorLEARN ABOUT INVASIVE SPECIESbreadcrumb separatorForest Pests and Pathogensbreadcrumb separatorEmerald Ash Borer Page

The Insect

Physical Description

Adults: bright metallic green wood-boring beetles, 8 -14 mm (about ½ inch) long and 3-3.5 mm (1/8 inch) wide, body elongated, head flat. The dorsal surface of the abdomen (underneath wings) is usually a bright red colour

Pupae: 10 -15 mm long, creamy white in colour.  As it develops, it takes on adult colouration

Larvae: 25 - 32 mm long at maturity, creamy white in colour, brown head, flat, broad shaped body; 10-segmented abdomen (bell-shaped segments) and a fork-like appendage on the tip of the abdomen. 

Photo provided by Taylor Scarr, OMNRF
Photo provided by Taylor Scarr, OMNRF

Emerald ash borer adult and larvae (left), and adult with extended wings (right)

Life Cycle

Adult beetles actively feed on host plant foliage throughout their lives. Adults lay eggs in crevices on host tree bark or under bark scales; peak oviposition period typically occurs between late June and early July in temperate regions (Bauer et al., 2004) but may vary depending on factors such as latitude and local climate. To hatch, larvae chew through the side of the egg that is stuck to the bark, and bore into the sapwood, phloem, or cambium part of the bark, where they form pupal chambers and overwinter. When EAB populations become large enough, larval feeding under the bark girdles the tree, eventually leading to tree death. Pupation occurs in the early spring. When development is complete, the adult EAB will chew out of the bark of the tree, leaving a distinctive D-shaped exit hole in the bark (Bauer et al., 2004). Adult EAB begin to emerge from trees in late spring, depending on temperature, and are able to fly immediately after emergence.

Host Trees

EAB attacks and kills all species of North American ash (Fraxinus spp.) that it has encountered. A total of 20 species of ash are found in North America, six of which are native to Canada: green ash (F. pennsylvanica), white ash (F. americana), black ash (F. nigra), and much less common blue ash (F. quadrangulata), pumpkin ash (F. profunda), and Oregon ash (F. latifolia) in B.C. Blue ash may succumb to EAB, however, research indicated that it is mostly resistant. Recent evidence from the U.S. suggests that EAB may also attack the white fringetree (Chionanthus virginicus). Fraxinus and Chionanthus both belong to the olive family (Oleaceae), so likely have similar chemical composition and lack of appropriate defenses.

 Photo: Karan A. Rawlins, University of Georgia, bugwood.org 

The green ash (Fraxinus pennsylvanica), pictured above, is a preferred host tree of the emerald ash borer.

Signs & Symptoms

Signs and symptoms include (FIAS, NRCan, 2013):

  • Crown dieback

  • Bark deformities

  • Woodpecker feeding holes

  • D-shaped exit holes in the tree

  • Epicormic branches (shoots growing out of the lower trunk (commonly), but can be found on all parts of the trunk or branches)

  • Yellowing of foliage

  • Vertical cracks in the trunk 

Photo: Taylor Scarr, OMNRF (edited) 

Galleries formed under the bark from EAB larval
feeding. D-shaped exit holes are circled in red.