The emerald ash borer (Agrilus planipennis, EAB) is a metallic-green beetle from East Asia whose larvae kill ash trees by feeding under the bark. First found in Michigan in 2002, it has killed millions of ash trees in North America and is spreading westward from Moscow. Wood packaging, together with nursery stock and logs, is one of the recognized pathways, and ISPM 15 treatment and debarking are the main defenses on the packaging side.
What the beetle does
Adult EAB are slender, about 8 to 14 mm (0.3 to 0.55 in) long, and bright metallic green. They feed on ash leaves, but the damage comes from the larvae. Females lay eggs in bark crevices; the larvae tunnel through the thin layer of living tissue between bark and wood (the phloem and cambium), carving winding, S-shaped galleries that cut the tree's transport system. The adult leaves a small D-shaped exit hole.
Infested trees lose their crowns over a few years and often die within several years of first attack. The key feature is that EAB attacks healthy trees, not only stressed ones, which is why it behaves as an aggressive invader.
Susceptibility differs by region:
| Ash group | Susceptibility |
|---|---|
| North American ash (e.g. green and white ash) | Highly susceptible |
| European ash (Fraxinus excelsior, F. angustifolia, F. ornus) | Susceptible |
| Asian ash species | Relatively resistant, having co-evolved with the beetle |
History of the invasion
The beetle's native range covers China, Japan, Korea and the Russian Far East. It reached North America before it was noticed: the first detection was in southeast Michigan in 2002, and the beetle had probably been present for years. It has since spread across much of the eastern United States and Canada, killing millions of trees.
In European Russia, EAB was reported from Moscow in 2007, though specimens date from 2003 or 2004 and it probably arrived earlier. Forest Research (UK) summarizes that by 2013 it had been found at least 200 km south and west of Moscow, with spread of roughly 30 to 40 km a year, mostly human-assisted rather than natural flight. The same review expected arrival in the European Union within years, which makes EAB a priority concern for European forest health agencies.
Pathways: packaging, plants and logs
Analyses of the Moscow outbreak identify several routes:
- Wood packaging material, such as cable spools, pallets and wooden crates, made from ash or containing ash components.
- Imported nursery stock of ash, especially green ash (Fraxinus pennsylvanica), widely planted in Russian towns and along roads.
- Logs and firewood moved by rail and road, including via the Trans-Siberian railway.
Because EAB larvae feed in the layer just beneath the bark, the two ISPM 15 measures most relevant to it are debarking and treatment. Removing bark takes away most of the habitat, and heat treatment at 56°C core temperature for 30 minutes kills larvae in the remaining wood. See debarking requirements and heat treatment.
Pallet-grade lumber often contains mixed hardwoods, and ash can be present among them. Ash is one of the hardwoods that can turn up in mixed-hardwood pallet stock. Pallet makers in infested regions therefore have a practical interest in treatment and in knowing the origin of their raw material; see pallet wood species.
Ash dieback is a different problem
EAB is often confused with ash dieback, but they are unrelated. Ash dieback is a fungal disease caused by Hymenoscyphus fraxineus, which has spread across Europe from the east and affects European ash. EAB is an insect that bores under the bark. The two can occur together, and researchers note that trees weakened by dieback may be more vulnerable to EAB.
Other wood-boring pests in packaging
EAB is one of a group of insects and fungi that ISPM 15 targets. Others include:
| Pest | Group | Notes |
|---|---|---|
| Asian longhorned beetle | Longhorn beetle | Kills hardwoods; spread to the US and Europe in packaging from China |
| Pinewood nematode and Monochamus vectors | Nematode and longhorn beetle | Kills pines; Asia and Iberia |
| Sirex noctilio | Woodwasp | Attacks pines; established outside its native Eurasia in several southern hemisphere countries |
| Bark beetles (e.g. Ips spp.) | Scolytinae | Live under bark of conifers; debarking is the main control |
| Agrilus relatives such as A. cyanescens | Jewel beetles | Related to EAB; found in Europe |
Many of these species are not detected until they become established, which is why the standard treats all raw solid-wood packaging, not individual species, as a risk. A pallet's species, origin and treatment history are more useful signals than an assumption about which pest is "in season".
What shippers and pallet producers can do
- Require the ISPM 15 mark on all solid-wood packaging; see the ISPM 15 mark.
- Check bark and exit holes on incoming pallets. D-shaped holes in ash wood or galleries under residual bark should lead to rejection and a report to the plant protection authority.
- Avoid moving untreated ash wood and firewood out of quarantine zones; many jurisdictions in North America regulate ash movement.
- Keep records of wood origin, so that a suspect batch can be traced back to a sawmill; see pallet quality control.
Frequently asked questions
Does ISPM 15 stop emerald ash borer?
It reduces the packaging pathway by requiring debarked wood and heat treatment or an equivalent approved measure. It does not stop spread through firewood, logs, nursery stock or the beetle's own flight.
Are ash pallets a particular risk?
Untreated ash wood with bark is the highest risk, because larvae live just under the bark. Treated, debarked and marked ash wood is treated like any other compliant packaging.
Is emerald ash borer in Europe?
It is established in European Russia around Moscow and surrounding regions, and European authorities consider it a major threat. Its distribution keeps changing, so current records from EPPO or national plant protection services should be checked.
What is the difference between EAB and ash dieback?
EAB is an insect whose larvae bore under ash bark. Ash dieback is a fungal disease that kills shoots and crowns. They are different organisms, though both harm ash.
Sources
- Emerald ash borer in Russia (Williams, Forest Research, 2017) — Forest Research (UK)
- ISPM 15: Regulation of wood packaging material in international trade (2009) — International Plant Protection Convention (FAO)
- Wood Packaging Material — USDA APHIS