Spruce Bark Beetle and Wood Boring Insects

Observation by Nick Treinen:

As the images show, I am observing spruce bark beetle larvae coincident with the larvae of a wood boring insect. I would estimate the relative abundance in one square-foot section of this tree to be 60 bark beetles to 4 wood borers.

The spruce bark beetle epidemic currently ravaging Southcentral AK's spruce trees is well-known, but I haven't heard mention of other pests occurring in conjunction.

This summer has been exceptional for high temperatures and low rainfall, which may relate to the severity of these insect infestations.

Comments from LEO Editors:

This observation was sent to the UAF Cooperative Extension.

Jessie Moan, Forest Health Technician at the University of Alaska Fairbanks Cooperative Extension Service, writes:

The labeling is mostly correct, but what is labeled as spruce beetle larvae are actually pupae (that next stage after larva before adult). These pupae would likely have turned into adults in the next couple of weeks. The adult circled in the first picture is very brand new adult which is why it is a light tan color. In the third picture, the white insect is a very very very new spruce beetle adult. The other insect circled in purple is a wood borer larva.

To the question about what species the wood borer is, I'm not certain. I do think it is one of our roundheaded wood borers (the adults are called longhorned beetles), but I don't have a species for you. The larvae can look very similar.

These pictures show a really interesting part of the lifecycle most people don't ever get to see because it is all occurring beneath the bark!

To the observation about other things occurring in conjunction with spruce beetle, there's actually lots of things that can and will get into spruce trees, including wood borers and other bark beetle species. These are mostly considered secondary because they are not killing trees but rather move in once the tree is dead or dying. The same types of insects would be found in a tree that was killed by fire or blew down in a wind storm.

Comments from LEO Editors:

According to a US Forest Service publication on Roundheaded Wood Borers, they will attack stressed, dead, or dying, trees. The beetles introduce yeasts, bacteria, and wood-rotting fungi that assist in the decomposition process. Larvae will overwinter under the bark, and will help the tree decompose over several years. Erica Lujan

For more information about pest management, see the UAF Cooperative Extension Service website. See also a video on how to submitting insect samples for identification.