Found throughout conifer forests of North America, white-spotted sawyer beetles (Coleoptera: Cerambycidae: Monochamus scutellatus) are economically important tree pests. They attack several species of pines (Pinus spp., Pinaceae) and spruces (Picea spp., Pinaceae) as well as balsam firs (Abies balsamea, Pinaceae), often causing significant injury and monetary losses from harvested lumber.
Large adult beetles feed on needles and young twig bark, but the real damage is caused by their larvae. Mating and egg laying occurs from June to September, with females depositing eggs in holes they have chewed through bark on the thick trunks. After larvae hatch they feed on the wood, excavating galleries of tunnels as they move along. These wounds make the trees susceptible to infestation by pathogenic fungi that cause even more damage.
The pitting and discoloration these beetles and their associated fungi cause both injures trees and negatively impacts the value of affected lumber. Insecticides are often used to reduce the beetle population, but in the absence of human intervention these insects have an interesting way of controlling their own populations. Cannibalism is a frequent occurrence among larvae. Whenever two individuals stumble across each other while excavating tunnels, one usually eats the other. Larvae suffer a 70% mortality rate just from natural causes like this.