In the order of Coleoptera, under the family of Scolytidea, there is a collection of a variety of beetles known as bark beetles. There are approximately 600 different species falling under this heading. In appearance bark beetles are usually between the lengths of 1/8" and 1/3", black or brown in coloring, cylindrical, with a hard shell. Despite their name, they do not bark. However, they do live underneath the bark of trees. Most bark beetles inhabit only dead or dying trees, or tree parts still containing bark. Unfortunately, there are some particular species that do attack otherwise healthy trees.
The life cycles for the various bark beetles are very similar. A female adult beetle searches for an appropriate nesting area for its particular species, and, upon finding it, proceeds to burrow through the bark into the inner layer of the tree. Once established underneath the bark, she emits a pheromone that attracts both male and female beetles alike. Once other beetles are attracted, they pair off, and construct egg galleries within the tree. Afterwards, they lay their eggs on alternating, opposing sides of the gallery. When the eggs hatch into larvae, they proceed to eat their way outward from the gallery, often moving closer towards the bark as they do so. After the larvae have fully developed, they create a pupal chamber at the end of the feeding tunnel. Once this tunnel is created, the larvae pupates into an adult beetle, which will eventually fly off in search of a new host, restarting the entire cycle.
While most bark beetles do prefer dead and dying trees, there are a few notable exceptions that will occasionally attack healthy trees. Some, such as the elm bark beetles, also present a secondary problem in that they may transmit diseases, like Dutch Elm Disease. Most species also have specific type of trees they prefer to nest within, and are often named for that particular tree. Some examples of the damaging versions of these are the Southern Pine Beetles, Mountain Pine Beetle, Douglas-fir Beetle, Western Balsam Bark Beetle, Hickory Bark Beetle, Ash Bark Beetle, Birch Bark Beetle, and the Spruce Beetle. A few other harmful bark beetles include the Ips Beetle, or engraver beetle, and the Black Turpentine Beetle, both of whom attack pines. There is also the Shothole Borer who attacks fruit, wild cherry, elm, and serviceberry trees. The Peach Bark Beetle seeks out elm, mulberry, stone fruit, and mountain ash trees.
The most effective treatment for an outbreak of bark beetle infestation is prevention. This is due to the fact that most bark beetles will not attack healthy trees, unless there is an excessive amount of bark beetles in that area. Therefore, by removing the beetles breeding grounds to keep population in manageable limits, the problem is solved before it ever happens. This can be done by eliminating dead, dying, and unhealthy trees, and also by removing bark from firewood and other scrap pieces of wood. In the proper amounts, bark beetles are usually a very valuable part of a forest's ecosystem, helping to remove trees and limbs that are already weakened or diseased.
information culled from:
www.ext.vt.edu/departments/entomology/factsheets/barkbeet.html
www.for.gov.bc.ca./tasb/legsregs/fpc/fpcguide/beetle/chap1.htm
www.for.gov.bc.ca./tasb/legsregs/fpc/fpcguide/beetle/chap2.htm
www.idahoforests.org/health.org/health4.htm