Pheromone Composition of the Eastern Larch Beetle Dendroctonus simplex Leconte (Coleoptera: Curculionidae): Quantitative Analyses and Olfactory Responses

The eastern larch beetle, Dendroctonus simplex LeConte, colonizes tamarack, Larix laricina (Du Roi) K. Koch, and has become a major tree killer in parts of its temperate North American range. To fill existing gaps in knowledge of this insect's pheromone system, we used gas chromatography-mass spectrometry to perform quantitative studies of pheromone production by unfed beetles of both sexes, founding females excised from newly established galleries in a tamarack log, and both sexes excised post-pairing. To identify olfactory stimulants and thereby possible, additional pheromone components, we performed gas chromatography-electroantennographic detection analyses with antennae of both sexes exposed to volatiles collections from the beetles. We also exposed unfed male and female beetles to juvenile hormone III (JH III) to identify pheromone components regulated through this mechanism. Both female and male beetles exhibited antennal responses to 1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane (frontalin), 3-methylcyclohex-2-en-1-ol (seudenol), and 3-methylcyclohex-2-en-1-one (MCH) in volatiles of solitary mining females. Within approximately 24 h of joining a male, female production of seudenol and MCH largely ceased while production of frontalin continued. Unfed females produced no more than minute amounts of pheromone, and application of JH III induced production of frontalin from some females but not seudenol or MCH. Unfed males and males exposed to JH III produced almost no volatiles, whereas paired males produced minute amounts of frontalin (possibly an artifact), no seudenol or MCH, and some oxygenated monoterpenes. We found that timing of production of certain pheromone components was inconsistent with their known activity.