Pheromone biosynthesis by selected species of grain and bark beetles

The overall goal of this thesis was to investigate pheromone biosynthesis in grain and bark beetles.Insects were exposed to either radio-or stable isotope-labelled precursors.Incorporation of label into pheromones was determined by scintillation counting or gas chromatography/selected ion monitoring-mass spectroscopy, respectively.Most known aggregation pheromones of cucujid grain beetles are macrolides, called "cucujolides".Objectives of this project were to determine the biosynthetic origin of these cucujolides and to study the mechanism of cyclization.Studies were performed on Oryzaephilus mercator (Fauvel) and/or Cryptolestes ferrugineus (Stephens).In C. ferrugineus, cucujolide I (numbered according to J. Chem.Ecol., 1988, 14:2069-2096) was of terpenoid origin.Cucujolides 11, 111, IV and V were found to be of fatty acid origin.The de novo biosynthesis of all cucujolides (I through V) was detected.The cyclizations of the hydroxy acid precursors to form I in C. ferrugineus, and I1 in C. ferrugineus and 0. mercator, proceeded with retention of the hydroxyl oxygens.The cyclic ketals exo-and ends-brevisomin are p h e r ~m 0 n e ~ of many economically important scolytids.The objective of this project was to study brevicomin biosynthesis in the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins and the western balsam bark beetle, Dryocoetes confusus Swaine.Insects exposed to (2)-or (E)-D2-nonen-2-one produced exo-or endo-brevicomin, respectively, that were clearly enriched in two deuterium atoms.The D2-exo-brevicomin produced by male MPB was found to be of the natural (+)-chirality by complexation chromatography.The biosynthetic transformation apparently proceeds through a keto-epoxide intermediate.Both oxygens of brevicomin are derived from molecular oxygen.Ipsdienol is a common bark beetle pheromone.The chirality of ipsdienol varies widely between different species, populations and even individuals.The objective of this project was to test the hypothesis iii that increased activity of the oxidation/reduction equilibrium between ipsdienol and ipsdienone effects a larger proportion of S-(+)-ipsdienol.The study insects were Dendroctonus ponderosae Hopkins, two populations of Ips pini (Say), and Ips paraconfusus Lanier.The hypothesis was disproved.