Bark Beetles by New Mexico State ForestryBark beetles, also called engraver beetles, attack ponderosa and pinyon pines as well as other conifers. Dendroctonus beetles attack medium to large ponderosa pine, blue spruce, Engelmann spruce, and Douglas-fir trees in New Mexico. Different species within the genera are difficult to distinguish based on body shape alone. Host species attacked, location, and shape of tunnels (egg galleries) they excavate are all important clues in identifying the pest species.
The initial attack on the tree is made by a few adult beetles. Once a tree is selected, the beetles produce an "aggregation" pheromone, drawing many beetles to the tree. The attack on the tree may be initiated by the male or by the female beetle. The beetle chews through the bark and excavates a chamber in the moist tissue beneath the bark. The opposite sex then enters the chamber and mating occurs. The female beetles then excavate distinctive tunnels or egg galleries under the bark. Eggs are laid in niches along the lateral walls.
Adult beetles may introduce a number of microorganisms into the tree when they attack. Some species have evolved specialized pockets for carrying such microorganisms as fungi, yeasts, and bacteria. Introduced blue-stain fungi are particularly important in killing the tree and may provide nutrition for the developing brood.
After hatching, larvae bore away from the egg gallery at right angles. They molt the three or four times and then construct a pupal cell either in the phloem or in the bark.
Bark beetles usual attack severely weakened or damaged mature or over-mature trees. Trees damaged by lightning or harsh weather and tree stressed from transplanting, logging slash, and recently cut firewood are prime candidates for bark beetle colonization. Vigorously growing trees have active resin systems that deter such colonization. When the beetle bores into a healthy tree, resin exudes from the wound and may prevent the beetles entry. The resin may also inhibit the spread of fungus that aids the beetle in killing the tree. When populations of bark beetles are very high, particularly around an outbreak, trees may be attacked by so many beetles that even healthy trees succumb.
The symptoms of an attack is the foliage high in the tree begins to fade, turning from green to yellow or red. Boring dust, a sawdust-like material pushed out of beetle galleries, can often be found around the base of the tree, in bark crevices beneath entrance holes, and on tops of branches where they intersect the trunk. Globules of resin called "pitch tubes", produced as the trees defense, may or may not be present. Woodpecker activity on the trunk is also a good indication that the tree has been attacked.
Once a tree has been successfully attacked by bark beetles, it cannot be saved. Infested trees should be removed, burned, or buried as soon as possible to protect surrounding trees from attack by emerging beetles.