Per IVARSSON, Gary J. BLOMQUIST and Steven J. SEYBOLD
University of Nevada Reno, Mail stop 330, Rena, Nevada 89557 00t4, USA
The aggregation pheromone produced by male Ips spp. accumulates in the hindgut and is released from the pellets as the beetles feed in the host tree phloem. The anatomical location of pheromone production in bark beetles is not known, and a number of studies have failed to demonstrate the presence of a hindgut-associated pheromone gland in these insects. We have developed an in vitro method for studying pheromone production by two North American species: The pine engraver beetle Ips pini (Say) and the California five-spined ips, Ips paraconfusus Lanier. When incubated with [1-14C]acetate, homogenized male I. pini tissue produces 14C-ipsdienone, while male I. paraconfusus tissue produces 14C-ipsenone. The main pheromone components of these species are the corresponding alcohols, ipsdienol and ipsenol. Addition of antioxidant to the in vitro assay did not lead to production of radiolabeled alcohols, suggesting that the ketones are not oxidation artifacts of our procedure. The ketone may be formed in one tissue and then transported to another tissue for the final reduction step to the alcohol. Furthermore, the chirality of the alcohols may be determined as the ketone groups are reduced to the alcohol. In the homogenized tissue such transport mechanisms are disrupted. Juvenile hormone (JH) stimulated in vitro ketone production when it was administered to live beetles 48 h before the assay. JH has previotusly been shown to induce ipsdienol production in vivo. Thus, the induction of ipsdienone and ipsenone production by JH provides further evidence that the production of the ketones is related to pheromone production.
This assay provides a tool to further investigate the pheromone system of bark beetles and to begin isolating the key enzymes and intermediates. Localization of the site of pheromone production, either by insect tissue or associated microorganisms is a primary focus of our research. It will also facilitate the study of the endocrine regulation of bark beetle pheromone production to determine which enzyme activities are induced by JH.