Emerald Ash Borer
Agrilus planipennis
📖 Description
The emerald ash borer is one of the most destructive invasive insects in North American history, having killed hundreds of millions of ash trees since its discovery in 2002. Native to Asia, it arrived in packing material and has since spread to over 35 states and 5 Canadian provinces. Ash trees have virtually no natural resistance to this beetle, and untreated infested trees have a near-100% mortality rate within a few years. The larvae feed on the inner bark (phloem) in serpentine galleries that girdle the tree, cutting off nutrient and water transport. By the time canopy symptoms appear, the tree is usually heavily infested and treatment options are limited.
⚠️ Symptoms to watch for
- D-shaped exit holes in bark (approximately 3-4 mm wide),Canopy thinning and dieback starting from the top,Bark splitting with S-shaped larval galleries visible underneath,Epicormic sprouting (water sprouts) on trunk and major branches,Increased woodpecker damage (flecking) on trunk,Tree death within 2-5 years of initial infestation
🩹 Treatment
- Apply systemic emamectin benzoate trunk injection every 2 years (chemical),Use imidacloprid soil drench for preventive treatment (chemical),Apply dinotefuran basal trunk spray (chemical),Release parasitic wasps (Tetrastichus planipennisi) as biological control (organic),Remove and destroy heavily infested trees before adults emerge (cultural),Apply biological controls like Oobius agrili for egg parasitism (organic)
🌿 Organic treatments
- Release parasitic wasps (Tetrastichus planipennisi) as biological control,Remove and destroy heavily infested trees before adults emerge (cultural),Apply biological controls like Oobius agrili for egg parasitism
🧪 Chemical treatments
- Apply systemic emamectin benzoate trunk injection every 2 years,Use imidacloprid soil drench for preventive treatment,Apply dinotefuran basal trunk spray
🛡️ Prevention
- Don't move firewood — this is the primary way EAB spreads,Treat valuable ash trees preventively with systemic insecticides,Plant diverse tree species to reduce vulnerability,Monitor with purple sticky traps and visual surveys,Report suspected infestations to local agricultural extension,Use only locally sourced or heat-treated firewood
🪴 Affected plants
- Ash Trees (all species),White Ash,Green Ash,Black Ash,Blue Ash
🦋 Natural predators
- Woodpeckers,Parasitic Wasps,Predatory Beetles
🌱 Host plants
- Fraxinus spp.
🔄 Lifecycle
- Adults emerge in late May through July, leaving distinctive D-shaped exit holes.
- They feed on ash foliage for 1-2 weeks before mating.
- Females lay 60-90 eggs in bark crevices.
- Eggs hatch in 7-10 days.
- Larvae bore through bark and feed on phloem in S-shaped galleries for 1-2 years.
- Pupation occurs in the outer sapwood or under bark in spring.
- Most populations have a 1-year lifecycle, but some take 2 years in cold climates.
- Adults live 3-6 weeks.
📅 Season
- Late Spring to Late Summer (adults); Year-round (larvae under bark)
🔎 Appearance
- Adults are brilliant metallic green elongated beetles with coppery-red or purple abdominal segments visible under the wing covers.
- Larvae are cream-colored, flattened, with bell-shaped body segments and a pair of brown pincer-like appendages at the tail.
- The distinctive D-shaped exit holes in bark are a key diagnostic sign.
💥 Damage level
- Severe
🔁 Reproduction rate
- Moderate
🗺️ Geographic regions
- North America
- East Asia
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