Endocrine regulation of de novo aggregation pheromone biosynthesis in the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae)

In vivo and in vitro radiotracer studies were conducted with the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae), to elucidate the relationships among feeding on host (Pinus jeffreyi Grev. & Balf.) phloem, juvenile hormone III (JH III) biosynthesis, and de novo aggregation pheromone (ipsdienol) biosynthesis. The in vivo incorporation of [1-C-14]acetate into ipsdienol by male I. pini increased with increasing dose of topically-applied JH III, demonstrating the stimulatory role by JH III in de novo pheromone production. In vivo incorporation of (RS)-[2-C-14]mevalonolactone into ipsdienol by male I. pini was not affected by increasing JH III dose. However, injection of [C-14]mevalonolactone resulted in significantly higher levels of [C-14]ipsdienol than those observed in saline-injected controls. This is direct evidence for the mevalonate-based isoprenoid pathway in de novo ipsdienol biosynthesis, and suggests that in this pathway JH III does not influence enzymatically-catalyzed reactions subsequent to the conversion of 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonate. An additional in vivo [C-14]acetate study demonstrated that de novo ipsdienol biosynthesis is also stimulated by feeding on host phloem. Lastly, an in vitro radiotracer study utilizing L-[methyl-H-3]methionine demonstrated that feeding stimulates JH III biosynthesis by the corpora allata (CA) of male, but not female, I. pini. Analysis by radio-high pressure liquid chromatography revealed that JH III is likely the type of juvenile hormone produced by the male CA. These data support a sequence of events leading to feeding-induced de novo pheromone biosynthesis in male I. pini: (1) feeding on host phloem; (2) feeding-dependent JH III biosynthesis by the CA; and (3) JH III-stimulated de novo ipsdienol biosynthesis. (C) 1998 Elsevier Science Ltd. All rights reserved.