In mid-May, 2010, I noticed our small forest had several medium-sized Ponderosa Pine with needles in varying stages of turning brown (seen in the tops of the two trees in the foreground of the photo on the left). Some needles were all brown; some still pale green and yellowing. These colors, present in all the needles of the tree, identify trees recently killed by beetles. At this time of year, trees with all needles uniformly reddish brown will usually have been killed the previous year. I cut the recently killed trees and used a drawknife to peel off the bark, exposing and killing the larvae. The photo on the right shows 3 larvae, about the size of a grain of rice.
The trees I cut and peeled had been attacked by beetles during the summer of 2009. Eggs laid under the bark hatched, and larvae fed on the life-sustaining, nutritive layers between the bark and wood. Inactive during winter, the larvae resumed feeding in the spring. By mid-May, the larvae were in oval cells where they will undergo metamorphosis and develop into mature beetles. The beetles will emerge from the bark during June and early July and attack healthy trees.My peeling away of the bark uncovered not only larvae and “pupae” (intermediate development stage between larva and adult) but also a few apparently fully developed, black beetles. Beetle maturation doesn’t take place in all beetles at identical times, even in the same tree. The few apparently mature beetles I found are described by my entomologist advisor, Amy Gannon (Forestry Division, Montana Department of Natural Resources and Conservation) as “teenagers”, not fully mature but almost. Other individuals will reach this stage at somewhat varying times. They remain under the bark for a time before penetrating to the outside and seeking a host tree for egg laying.
Besides killing the beetle larvae by cutting and peeling infested trees, I will put out patches of a synthesized hormone. Its naturally produced counterpart is an “anti-aggregation” hormone emitted by beetles in the process of attacking a tree. The hormone tells other beetles: “This tree is full, stay away!” The synthetic hormone is expected to repel beetles when properly placed: In a grid using 30-45 foot centers (30 patches per acre), one patch 6-10 feet high on the north side of each tree. The hormone must be put out at the right time because its activity fades with exposure. The time to put out the hormone patches in our area is July 1st(slightly before will be better than slightly later). It’s expensive (about $30 per box of 2 patches) so can only be used on small acreages where the trees have special value.