Bark Beetles (Scolytidae)
Bark Beetles
Scolytid bark beetles are insects that develop feeding on the cambium under the bark of trees. Typically the adult beetles first make distinctive galleries in which they mate and lay eggs. The larvae tunnel outwards from these galleries and can girdle the tree.
Another very important aspect of bark beetles is their involvement with various fungi, particularly those in the genera Ophiostoma and Ceratocystis. These include the fungi involved in Dutch elm disease and the 'blue stain' fungi of conifers. Bark beetles are very important in the distribution of these fungi to new trees. In many instances the two organisms - bark beetle and fungus - are very co-dependent. Bark beetles spread the fungus and the fungus helps to provide declining hosts that are optimal for beetle development.
Most bark beetle species successfully breed in trees that are severely stressed or dying. Newly transplanted trees are particularly susceptible to attack by these insects. Proper cultural practices to promote tree vigor are the most important means of preventing most bark beetle problems. Often, these techniques are sufficient for control.
A few bark beetles are capable of killing healthy trees, either through coordinated "mass attacks" (mountain pine beetle for example) and/or through introduction of disease causing fungi into healthy trees (elm bark beetles). Sanitation and insecticide applications are of great importance in managing these pest situations.
An active area of research develop involves the behavioral chemicals (pheromones) used by bark beetles to regulate their attacks. Both pheromones that are involved in attraction (aggregation pheromones) and pheromones that are repellent to bark beetles (anti-aggregation pheromones) have been identified for some species. These have promise in managing beetles when populations are not high, but have been generally ineffective in preventing attacks during outbreaks.
Bark beetle preventive insecticide applications involve a thorough wetting of the bark (point of run-off) prior to the egg laying period. Carbaryl (Sevin, Sevimol), chlorpyrifos (Dursban) and permethrin (Astro) are currently used for control of bark beetles.
Specific recommendations for bark beetle control are included in the supplement in the sections: Mountain pine beetle, European elm bark beetle, and Engraver (Ips) beetles.
