At first look, the galleries in the photograph above look a lot like one of the Dendroctonus bark beetles, such as spruce beetle (D. rufipennis). However, the wider, mostly-vertical egg galleries made by the parent beetles are mostly devoid of frass and there are cases where you can see two of these galleries come together to form a "tuning fork" or "V" pattern. These two characteristics, in combination with the scale of the photo make them Ips. The most likely species in spruce in Colorado is Ips pilifrons. This is limited to Engelmann spruce, although there is a subspecies in southwestern Colorado that is recorded from both Engelmann and Colorado Blue. Throughout most of the state, particularly in ornamentals, an ips beetle found in Colorado Blue is likely to be Ips hunteri. Its gallery pattern is more delicate than that shown and the overall pattern tends to look like "spaghetti" rather than dominated by short, wide vertical egg galleries with less obvious larval galleries coming off to the side.

More of the same. In this light, the lack of frass packed into the vertical egg galleries is even more obvious. This "house-cleaning" by the parent beetles is why more boring dust is produced outside the tree on the bark surface in the case of Ips vs. Dendroctonus (which have their egg galleries packed with brown frass).

Intact bark on the left, a narrow strip of Ips galleries in the middle and then large, fibrous boring dust on the right. These large fibers mixed with darker fine material are typical of longhorned wood borers in the family Cerambycidae. I feel almost certain the species involved in this case is Monochamus scutellatus, the whitespotted sawyer. This is a large dark gray borer with long antennae and sparse bright white spots on the wing covers. The beetle has the shine of pencil lead and the white spots look like spattered whiteout correction fluid. They are quite common as secondary invaders of trees killed by something primary like drought, bark beetles, herbicide exposure, etc. In an ecological sense, to the extent the borers "use up" the inner bark area prior to boring deeper into the xylem wood, they are beneficial by reducing the production of bark beetles from the trees they share.

The dime gives a good scale and is another indicator that the beetles emerging from the holes are too small to be spruce beetle. These holes are consistent for Ips. If this was Dendroctonus, the holes would be about as big as the flame in the torch on the dime.

Here is another good shot of the Ips galleries (main vertical galleries devoid of frass), not a lot of branching or forks, however, which could easily be confused with Dendroctonus.

to Trees and Shrubs of Western Colorado; Problems and Care

Placed on the Internet April 2, 2002