Conifer bark beetles are tree pests of the genera Dendroctonus, Ips, Scolytus who prey primarily on pines (Pinus) but also additional evergreens such as fir (Abies), spruce (Picea), arborvitae (Thuja), others. Trees that are already under stress from drought, insufficient root area or damage, transplanting or disease are at higher risk for a bark beetle infestation. Young, healthy trees produce adequate resin to repel a bark beetle attack, but older, wounded or weakened trees sometimes emit a volatile hormone which is strongly attractive to the beetles.
Bark beetles have been able to overcome natural protections by attacking en masse. Several beetles of the same species will find a target tree, they then emit an aggregation pheromone which is basically the equivalent of a group text to every other beetle in the vicinity. Countless insects arrive on the tree and begin burrow through the bark into the vascular tissue which causes the pitch to flow. The beetles will continue boring into the same spot, re-drilling holes when pitch hardens, and causing more and more to flow, eventually exhausting the tree’s supply. Once this natural defense is taken down, the insects are free to fully colonize the tree by the thousands and eventually kill it. Some bark beetles vector fungal spores which will infect the already weakened host tree and speed up the process.
The best prevention from a bark beetle invasion is consistent, effective, adequate tree care. Adjust your watering schedule based on current conditions; during times of drought apply heavy irrigation. Also, get your trees on a nutrient program, fertilizing once per year can help trees manage stress during times of weather extremes. Many of these species of beetle are more prevalent in coastal areas, if your property is in a region that experiences salt spray, washing foliage after a storm can help prevent salt burning and desiccation. In addition to these cultural practices, there are pesticides that can attain a level of control, contact your arborist with any questions or concerns about your conifer trees and potential bark beetle issues.