Bark beetles are among the most economically important forest pests in the northern hemisphere, and rely on monoterpenoid aggregation pheromones to coordinate host colonization and mating. In this study, we investigate the interplay between feeding on host phloem and the induction of de novo pheromone biosynthesis in Ips confusus, the pinyon Ips. I. confusus has become a major pest in the southwestern United States, destroying hundreds of thousands of acres of pinyon pines. Juvenile hormone (JH) III regulates pheromone production in a number of bark beetles. Interestingly, it appears that JH III alone does not stimulate pheromone biosynthesis in male I. confusus, but rather some other regulatory factor is required for pheromone production. We have found that feeding on host phloem, but not JH III treatment, strongly induces pheromone production in male I. confusus. In males, feeding also stimulates the activity of a number of mevalonate pathway enzymes including 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-R), which is thought to be the most highly regulated enzyme in the pathway. Nevertheless, feeding and JH III both significantly up-regulate mRNA levels of HMG-R and other mevalonate pathway genes.