Effects of Feeding and Mating on Pheromone Release in the Southern Pine Beetle1,2

Response of field populations of Dendroctonus frontalis Zimmermann to their aggregating pheromone was correlated with pheromone content of dissected hindgut tissues of adult beetles as determined by the gas-liquid chromatography (GLC) technique. Adult beetles in various stages of feeding activity and reproductive states were used for this purpose. Two major components of the aggregating pheromone, frontalin and trans-verbenol, were found in the largest quantities in emergent unfed females. After 48 hours of feeding, frontalin content of the hindguts was 29% and trans-verbenol content was only 5% of that of emergent females. Continuous bioassays of females feeding in host material showed increasing response of field populations to the beetles until 24-48 hours after feeding had begun, then response declined. The fact that pheromone content declined steadily following beetle attack while field response increased was thought to be clue to capture of the pheromone in frass particles, thus slowing its rate of release. The decline of pheromone components in hindguts of mated females was not precipitous or abrupt as suggested by behavioral studies on other species of Dendroctonus. Field bioassays confirmed the GLC studies and showed that in both virgin and mated females peak attractiveness occurred 24–48 hours after the tree was attacked by the beetles.