Emerald Ash Borer

• The adults' exit holes have an unmistakable D shape, and they are often the first proof that a tree has already been infested for years.
• In its native forests, in China and Korea, it is a rare and unimportant insect: it is the American and European ash trees that have no defences against it.
• It spreads above all through the movement of firewood, which is why many North American regions ban moving firewood between counties.
• It is one of the most destructive invasive forest species in history. It was detected near Detroit in 2002 and has killed hundreds of millions of ash trees in North America.
• By the time it was discovered it had been established for a decade: dendrochronological analyses showed it was already killing trees in Michigan in 1998, and it probably arrived in the early 1990s in wooden packaging from Asia.
• It kills almost everything it attacks: more than 95% of infested American ash trees die within two to five years. Asian trees, which coevolved with it, withstand it.
• In February 2025 it was present in 37 US states and six Canadian provinces.
• The adult flies little, less than a kilometre, so its rapid spread is explained above all by the human transport of firewood and nursery stock. Hence the campaigns against moving firewood between regions.
• It leaves a D-shaped exit hole, an unmistakable trace on the bark.
• In 2003 an invasion was simultaneously detected in Moscow, and both appear to stem from a single source in the late 1980s.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Ash trees in woodland, streets and parks

Size at birth

Egg 1 mm across, white when laid and amber before hatching; the mature larva reaches 26 to 32 mm

Sexual maturity

The females begin to lay about two weeks after emerging; the adult leaves through a D-shaped hole 3-4 mm wide, characteristic of the species

Gestation / incubation

The eggs hatch in 7-10 days, up to 15 in cold weather; the larva goes through four instars and its stage lasts about 300 days, from June to April of the following year. The full cycle takes one to two years depending on the climate and the vigour of the tree

Litter / clutch size

60 to 90 eggs per female over her lifetime, laid one by one in cracks in the bark of the trunk and the thicker branches; she can lay 1 to 23 at a time, although one is the norm

Sources consulted: Wikipedia (es): Agrilus planipennis · Lower Hudson PRISM, ficha Emerald ash borer · Forest Invasion (Chequia) (68-90 huevos) · Animal Diversity Web, Agrilus planipennis · Bugwoodwiki · Forest Invasion (Chequia) · IUCN GISD, ficha Agrilus planipennis · Forest Invasion (Chequia), ficha EAB · Bugwoodwiki, Agrilus planipennis

Best time: From May to July, when the adults emerge