Blue Stain Fungi on Cross-Section of Infected Pine Truck. Beetle infestations often begin on damaged or severely stressed trees. Odors emitted by trees struck by lightning, damaged by storms, mechanically injured by construction or harvesting equipment, or severely stressed by heavy pruning attract bark beetles from other places. Pines under any kind of stress are susceptible to attack by bark beetles, particularly under beetle outbreak conditions. Once on the tree, beetles bore through the bark to the cambium, mate and begin to construct galleries.
Healthy trees respond to beetle attacks by exuding copious amounts of pitch or sap.
The pitch and sap may exude from the entrance holes and harden on the bark surface to form pitch or resin tubes. Depending on species, either sex can begin the attack. Females that successfully infest trees, mate and lay eggs along the sides of the gallery. Eggs hatch in three to nine days into first-stage larvae. Bark beetles can also give off chemicals that inhibit the arrival of other beetles, preventing overpopulation of the trees by developing brood.