The Life Cycle of the Pine Beetle

Pine beetles are also known as bark beetles. The scientific name is: Dendroctonus ponderosae Hopkins. The pine beetle will complete its life span under the bark of a pine tree. There is an exception to the preceding rule, and that is when the adult beetle emerges, only to attack new trees.

The beetle is not a welcome insect. It spends its time infesting and killing such trees as the ponderosa, sugar, lodgepole, and white pine. The infestation of this insect generally occurs most frequently within lodgepole pine stands containing large sized trees or within the dense stands of ponderosa pine. Infestation by the beetle can cause large-scale tree destruction: in the millions to be precise.

A beetle infestation is not good news since during these outbreaks; the tree destruction can greatly alter the eco-system of the forest as a whole. This means, some forests are virtually stripped; resulting in areas of mere shrubs and grassland! Further, such an outbreak can completely change the habitation of wildlife in the area; since many species, beforehand, had counted on the forest as a form of protection or cover. Tree mortality can cause the water yield to naturally diminish, too.

The mountain beetle develops through four successive stages including: a) the egg, b) larva, c) pupa and d) the adult. All of these stages are spent under the bark of the tree it has infested. There is one exception; however—that being, as alluded above, the few days when the adult beetles emerge to fly to other trees.

During the first stage, female beetles create straight egg galleries: underneath the bark of the tree. The egg galleries are located within the inner bark; however, she may score the sapwood to some extent. The egg galleries range in size from four to forty-eight inches long; and on average they are ten inches long. The female beetle will then lay her eggs along the galleries she has created underneath the bark of the pine tree. She lays her eggs during the summer and autumn months.

The larvae are white with brownish heads; and have no legs. The larvae stage lasts for around ten months, generally from August to the next June. The larvae feeds on the phloem; creating additional galleries, in so doing, that extend: angled to the right of the egg galleries. The larvae, when mature, excavates oval shaped cells in order for the transformation of the third stage of pupae to take effect. Lastly, the beetle reaches the adult stage. All told: the entire beetle life cycle takes around one-year to complete.

The adult beetle feeds inside the bark of the tree before emerging. Emergence occurs after a number of feeding chambers coalesce. The emergence occurs, in groups, comprised of adult beetles. One or two of the adult beetles will make a hole within the bark in which to exit. After so doing, a number of the adults will fly out of this exit hole to attack new trees.

The harmful beetles contain spores of fungi on their bodies and in a special arrangement on their heads. The fungi interrupts the proper flow of water to the tree’s crown. The fungi also decreases the flow of the tree’s pitch. The two factors contribute to the eventual destruction of the tree.


Amman, Gene D., Cole, Walter E. Mountain pine beetle dynamics in lodgepole pine forest. Part II: population dynamics. Gen. Tech. Rep INT-145. Ogden, UT: United States Department of Agriculture, Forest Service, Inter-mountain Forest and Range Experiment Station; 1983 p. 59.