**Metallic Wood Borers** (family Buprestidae), also known as **Jewel Beetles**, are a diverse group of beetles named for the often bright, iridescent, metallic sheen of their bodies (green, blue, copper). The adults are minor pests, but the larvae (called **flatheaded borers**) are major, economically devastating pests. The larvae bore deep into the wood of trees and shrubs, creating winding, oval-shaped tunnels (galleries) that girdle the tree, obstruct nutrient flow, and compromise structural integrity, often resulting in the death of the host plant.
Taxonomy and Classification
Metallic Wood Borers belong to the order Coleoptera. They undergo complete metamorphosis. While many native species attack only dead, dying, or severely stressed trees, invasive species like the **Emerald Ash Borer** (*Agrilus planipennis*) are highly aggressive and attack healthy trees, causing massive ecological and economic loss.
Physical Description
Adult Metallic Wood Borers vary widely in size, from 1/8 to over 1 inch long.
- **Adult (Key ID):** Compact, bullet-shaped, and often brilliantly metallic-colored (green, copper, blue).
- **Larvae (Flatheaded Borers – Key ID):** Creamy white, legless, with a distinctly **flattened and widened area** just behind the head (thorax), giving them a mallet-head appearance.
- **Damage Sign (Key ID):**
- **D-shaped Exit Holes:** The emerging adult beetle chews a distinctive, perfectly **D-shaped** exit hole through the bark.
- **Winding Galleries:** Shallow, winding, frass-filled tunnels visible when the bark is peeled off.
- **Frass:** Fine, powdery sawdust mixed with excrement, often packed tightly into the galleries.
- **Conflict:** Severe forest, ornamental, and fruit tree pest.
Distribution and Habitat
Metallic Wood Borers are found globally. Their habitat is the bark and wood of their specific host trees, including hardwoods (oaks, ashes, maples) and fruit trees (peaches, apples). The larvae spend months or years tunneling under the bark.
Behavior and Conflict
The conflict is tree mortality from girdling.
- **Girdling:** The larvae tunnel through the phloem (nutrient transport) and cambium layers, effectively girdling the tree and starving it to death.
- **Structural Failure:** Larval galleries weaken the wood, making trees susceptible to breakage.
- **Invasive Devastation:** The Emerald Ash Borer has caused the death of tens of millions of ash trees, requiring billions of dollars in removal costs.
Management and Prevention
Control is integrated pest management (IPM), focusing on prevention and internal chemical control.
- **Maintain Tree Health:** Ensure proper watering and fertilization to deter native species that target stressed trees.
- **Do Not Move Firewood** from infested areas to prevent the spread of invasive species.
- **Systemic Insecticides:** Applied as a soil drench or trunk injection, these products move into the wood and kill the feeding larvae. This is the primary effective treatment for invasive borers.
- **Bark Sprays:** Applied to the trunk to kill egg-laying adults upon contact.
- Strict quarantines are often placed on infested regions to control the movement of wood products.
Conservation and Research
Metallic Wood Borers are managed as high-priority forest and ornamental pests. Research focuses heavily on biological controls for invasive species (parasitic wasps), developing resistant tree cultivars, and improving systemic treatment efficacy.