.. Journal of Chemical Ecology, Vol. 14, No. 2, 1988 TRAIL-FOLLOWING BEHAVIOR OF Reticulitermes hesperus BANKS (Isoptera: Rhinotermitidae) J. KENNETH GRACE, 1 DAVID L. WOOD, 2 and GORDON W. FRANKIE 2 1 Faculty of Forestry, University of Toronto Toronto, Ontario, Canada M5S 1A1 2 Department of Entomological Sciences, University of California Berkeley, California 94720 (Received November 25, 1986; accepted March 14, 1987) Abstract-The behavior of Reticulitermes hesperus Banks pseudergates (workers) was assessed on artificial trails containing different concentrations of steJ;"Ilal gland extract. On nongradient trails, more pseudergates were recruited to trails of greater pheromone concentration, they traveled a greater distance without pausing, and their rate of locomotion increased over that observed on trails of lesser concentration (positive orthokinesis). Of the indi- viduals pausing before completing trails of high concentration, fewer left the trails or reversed direction (negative klinokinesis) than on trails of lower con- centration. Termites walking down concentration gradients failed to complete these trails to the low-concentration termini. At a point representing an aver- age decrease of slightly more than 10-fold in the original concentration of pheromone, individuals reversed their direction of travel and returned to the high-concentration terminus. Termites walking up pheromone gradients pro- ceeded to the high-concentration termini without reversing direction. R. hes- perus pseudergates are thus able to orient along a gradient of trail pheromone by longitudinal klinotaxis. Key Words-Termite, Reticulitermes hesperus, Isoptera, Rhinotermitidae, pheromones, trail following, orientation. INTRODUCTION Reticulitermes spp. (lsoptera: Rhinotermitidae) establish chemical trails with pheromones secreted by the sternal gland, an epidermal gland located in the anterior portion of the fifth abdominal segment beneath the fourth abdominal sternite (Mosconi-Bernardini and Vecchi, 1964; Smythe and Coppel, 1966; 653 0098-0331188/0200-0653$06.00/0 © 1988 Plenum Publishing Corporation