Byers, J.A., & Birgersson, G. 1990. Pheromone production in a bark beetle independent of myrcene precursor in host pine species. Naturwissenschaften 77:385-387.

The two large pines in background are digger pine, Pinus sabiniana (at left) and ponderosa pine, Pinus ponderosa (at right).
Abstract-- Males of Ips paraconfusus (Coleoptera: Scolytidae) from the same brood source (ponderosa pine, Pinus ponderosa) were allowed to feed in five host pine species: ponderosa pine, Jeffrey pine, digger pine, lodgepole pine, and sugar pine. Surprisingly in contrast to the prevailing paradigm (that myrcene from pines is the precursor to pheromone components in Ips), the amounts of the pheromone components ipsenol and ipsdienol were about the same in beetles from each of the pine species. Attraction of beetles in the field to these infested logs were similar. However, the amounts of myrcene in the host logs varied from none detected by GCMS (gas chromatography mass spectrometry) to "large amounts". Thus myrcene from the tree does not appear to be significantly involved in the biosynthesis of the pheromone components. This also indicates that insect-plant coevolution of host tree selection (beetles could select trees high in myrcene precursor) and/or resistance (trees could lower myrcene to inhibit beetles from synthesizing pheromone) cannot be affected by variation of myrcene in the tree. On the other hand, alpha-pinene content in the host pine species was correlated with the production of cis-verbenol (the third pheromone component) by the beetles. But in all pine species there appears to be adequate amounts of alpha-pinene for pheromone component biosynthesis.
entire paper
Chemical Ecology