THE ORIGIN OF BARK BEETLE AGGREGATION PHEROMONES: NEWAPPROACHES, NEW RESULTS.
Steven J. Seybold
Dept. of Biochemistry/330, University of Nevada, Reno, Nevada 89557-0014.
Recent research has revealed that de novo pathways are centralto the biosynthesis of isoprenoid aggregation pheromones by scolytid barkbeetles. These results challenge the longstanding working hypothesis thatscolytid pheromone biosynthesis is dependent on toxic monoterpene precursorsfrom coniferous hosts. Studies with labelled 14C-acetate and 14C-mevalonateprecursors have directly demonstrated that the North American species Ipspini (Say) and Ips paraconfusus Lanier utilise the isoprenoidpathway to biosynthesise the aggregation pheromone components ipsdienoland ipsenol. Additionally, experiments with juvenile hormone III (JH III)and radiotracers have indicated that, like vertebrate cholesterol biosynthesis,the key regulatory enzyme in the pathway is HMG-CoA reductase. Furthermore,in vitro pheromone biosynthetic studies that yield the correspondingketones (ipsdienone and ipsenone) and analysis of messenger RNA for HMG-CoAreductase from pheromone producing Ips both suggest that the thoraxis the site of biosynthesis. Key questions that remain include: 1) Whatare the current and evolutionary interactions between de novo pathwaysand the well-studied transformations from host monoterpenes?; 2) Is JHIII sufficient for regulation of pheromone production or does a (presumablypeptide) brain hormone regulate biosynthesis of JH III?; 3) Do Dendroctonusspp. produce the bicyclic acetal pheromone component frontalin from anisoprenoid or fatty acid de novo pathway?; 4) Is de novo synthesisinvolved in the production of cis- and trans-verbenol or are they solelyderivatives of host ?-pinene?; 5) Are microbial symbionts involved in thesede novo pathways?