Olfactory orientation responses by walking femaleIps paraconfusus bark beetles I. Chemotaxis assay.

Gas-liquid chromatography of the air within the arena developed for this assay showed that a concentration gradient was established within 1-2 min of applying the pheromone (ipsenol, ipsdienol,cis-verbenol), and that this gradient was nearly constant for 20-95 min after application. The concentration fell rapidly and approximately exponentially between the source and the center of the arena. Turning rate and the number of beetles that reached the source increased, and heading with respect to the source decreased, in the presence of pheromone. Responses of beetles that did and did not reach the source were significantly different, but within each group there were no significant differences among dosages. Turning rate and heading varied little with distance from the source, while walking rate decreased as distance from the release point of the beetles increased. We hypothesize that dosage exerts its major effect on source location by altering the probability that a beetle will enter into orientation behavior and that beetles orienting to sources have similar behaviors even when orienting to a wide range of dosages.