Pheromone Biosynthesis in the Bark Beetle, Ips Paraconfusus, during Feeding or Exposure to Vapours of Host Plant Precursors

The quantities of trans-verbenol, myrtenol, and the pheromone, cis-verbenol, in the hindguts of males and females were found to increase in linear proportion following exposure to increasing concentrations of vapour of the host plant precursor, (-)-a-pinene. Males produced significantly more of these compounds than females. Differences between males and females in the ratios of compound production were indicated. The concentrations of myrcene, a-pinene, and other monoterpenes volatilized in male nuptial chambers in ponderosa pine were quantified as well as the amounts in phloem. Males do not appear to ingest sufficient phloem to obtain enough of the host plant precursor, myrcene, to account for production of the pheromones, ipsenol and ipsdienol, but they may consume additional amounts of myrcene in oleoresin/xylem. Comparisons of ipsenol, ipsdienol and cis-verbenol production in males when feeding or exposed to precursor vapours at various concentrations indicate that under natural conditions myrcene used in pheromone biosynthesis primarily enters the beetle via the digestive tract. Key Word Index: Ips paraconfusus, Pinus ponderosa, pheromone biosynthesis, bark beetle, myrcene, a-pinene, monoterpenes, ipsenol, ipsdienol, cis-verbenol, trans-verbenol, myrtenol, attractants, pheromones.