**Underbark Beetles** generally refers to several families of beetles that tunnel beneath the bark of trees, primarily the **Bark Beetles** (Curculionidae: Scolytinae) and certain **Flatheaded Borers** (Buprestidae). The conflict is **tree mortality**: these insects bore through the bark and excavate characteristic galleries in the phloem and cambium layer, effectively **girdling** the tree and cutting off nutrient and water flow, often leading to tree death in a single season.
Taxonomy and Classification
This group includes thousands of species in the Order Coleoptera (Beetles), often categorized as wood borers. They undergo complete metamorphosis. Many are highly specialized to specific tree genera (e.g., Pine, Spruce, Ash).
Physical Description
Adults are tiny (1\text{ mm} to 10\text{ mm}).
- **Adult (Key ID):** Small, cylindrical (Bark Beetles) or flattened and metallic (Flatheaded Borers).
- **Larva (Key ID):** Small, white, legless grub (Bark Beetles) or the flattened, segmented “flathead” larva (Borers).
- **Damage ID (Key):** Distinctive, patterned **galleries** scored into the sapwood beneath the bark; fine, reddish boring dust (**frass**) on the bark surface; pitch tubes on conifers; small, round exit holes.
- **Conflict:** Forestry, Ornamental.
Distribution and Habitat
Found globally. Habitat is the subcortical tissue (phloem/cambium) of both living and recently killed trees, depending on the species.
Behavior and Conflict
The conflict arises from their mass attack strategy and disease transmission.
- **Mass Attack:** Bark beetles release aggregation pheromones to signal other beetles to attack a tree simultaneously, overwhelming its defensive resin flow.
- **Disease Vector:** Many bark beetles (e.g., Southern Pine Beetle) carry and transmit pathogenic **blue-stain fungi**, which aid in killing the host tree.
Management and Prevention
Management is **Prevention and Sanitation**.
- **Sanitation:** Rapid removal and destruction (chipping/burning) of infested or dead trees to prevent beetles from completing their life cycle and emerging.
- **Tree Health:** Maintaining tree vigor through proper watering and avoiding drought/stress.
- Preventative application of contact insecticides to the bark of high-value trees to deter colonization.
Conservation and Research
Research is critical due to climate change exacerbating outbreaks. Focus includes modeling population dynamics, utilizing semiochemicals (pheromones) for trapping, and identifying beetle-resistant tree genetics.