Skip to: content | sidebar

EAB Main> Municipalities>

Emerald ash borer identification and biology

Adult EAB are about 10-13 mm long, cylindrical (somewhat bullet-shaped), and metallic emerald green. When the elytra (hard wing covers) and wings are pulled back a metallic pinkish-red colour is seen on the upper part of the beetle’s abdomen. The male and female beetle look similar to each other. The adult beetles can be seen from late May until August, depending on the temperature conditions in your area.

adult EAB beetle showing red abdomen Adult emerald ash borer beetle showing reddish abdomen.
Image: David Cappaert, Michigan State University,

After mating, and feeding for about 10 days, the female beetle lay eggs individually in bark crevices or slits, or under flaps in the tree's bark[28]. The tiny, oval eggs (about 1.2 mm long) are well hidden, so they are difficult to detect[28]. The eggs are white when they are first laid but turn brown after a few days[28]. Females lay eggs on all sides of the tree, but they prefer sun-exposed sides[28]. They are also observed to lay more eggs on rougher bark[4]. The estimated number of eggs that each female can lay is variable, from 33 to 68-90 eggs[3,28].

EAB eggs Emerald ash borer eggs are white when first laid and turn brown after a few days.
Image: Debbie Miller, USDA Forest Service,

Larvae hatch from the eggs after about 2-2.5 weeks. Larvae are translucent white, flattened, and relatively thin. Larvae have ten trapezoidal segments, the last having two dark brown spines[28]. EAB has four larval stages (instars), so four distinct sizes of otherwise similar looking larvae can be found; fully-grown larvae are up to 30 mm or more long. The entire larval stage lasts 300 days or longer[22,28].

EAB larva Emerald ash borer larva with 10 trapezoid-shaped segments.
Image: Chris Gynan, Silv-Econ Ltd.

The newly hatched larva bores through the tree bark into the inner bark layer of the tree where it feeds in the phloem and outer sapwood throughout its larval stages[28]. Larvae feed in a serpentine pattern either up or down the tree typically leaving a distinctive S-shaped gallery in their wake; this gallery is distinctive and when found under ash bark is a good indicator that the tree is infested by EAB[28]. Some larvae feed in a more linear fashion, especially in smaller diameter stems or branches[28]. Regardless of its shape, the feeding gallery becomes wider along its length as the larva grows larger, and the gallery is filled with a fine frass (which looks like sawdust) that the insect excretes as it feeds. Larvae bore into the sapwood or into the bark (approx. 1-7 mm) to overwinter and to pupate[3,28].

EAB larval gallery Serpentine emerald ash borer gallery.
Image: Troy Kimoto, CFIA

The pupae are the same shape as the adult beetle but are white when newly formed and then start to look like adult EAB as they develop. After the pupal stage is completed (5-13 days), the adult EAB emerges in the spring, boring out of the overwintering chamber and through the tree bark[28]. This leaves a distinctive D-shape exit hole in the bark (approx. 3.6 mm by 2.8 mm), evident from the outside of the tree[28].

EAB pupae and adults Emerald ash borer pupae and adults showing the progression of maturation.
Image: Debbie Miller, USDA Forest Service,

Adult EAB feed on ash leaves, this feeding damage is visible on the edges of leaves but the feeding damage is minor[28]. Adults only live two to three weeks. They prefer warmth and are more often found on the sun-exposed side of the tree so trapping and sampling techniques are more successful when conducted here.

EAB exit hole Typical D-shaped exit hole made by emerald ash borer adult emerging from the tree.
Image: Kathleen Ryan, Silv-Econ Ltd.

The entire emerald ash borer (EAB) lifespan usually lasts one year, but some EAB need two years to develop; the one-year life-cycle results in faster population growth than the two-year[22,31]. Two-year development is common at sites with lower populations of the insect; conversely, larvae develop more quickly in stressed ash trees[31]. Other factors such as climate could affect the beetle’s development time.

Emerald ash borer is a proficient flyer and can disperse naturally, but the rapid increase in range of the beetle is primarily because it is moved in infested firewood and possibly in nursery stock[22]. In the laboratory, the beetle can fly up to 2.8 km a day for up to four days (max flight 9.8 km overall) on a flight mill but other estimates suggest that mated females could fly over 20 km per day in natural situations[32,33].

See a simpler version of EAB biology.


Return to top