Sex pheromone of the plant bug, Phytocoris calli knight

Female Phytocoris calli Knight produce a sex pheromone from metathoracic scent glands. The pheromone consists of hexyl acetate (HA; present in both sexes), with the female-specific compounds (E)-2-hexenyl acetate (E2HA), octyl acetate (OA), and (E)-2-octenyl acetate (E2OA). HA and E2OA are key components of the pheromone, since deletion of either ester from the blend resulted in a total suppression of conspecific male trap catches. However, the binary blend of HA and E2OA was only slightly attractive to males, and was significantly less active than the four-component blend. The two ternary blends, HA/OA/E2OA and HA/E2HA/E2OA, were each as attractive as the full four-component blend. Evidence from previous research on the pheromones of Phytocoris species suggests that the apparent chemical redundancy in the pheromone of P. calli may actually be involved in maintaining reproductive isolation from other sympatric species. The patterns observed for pheromones of the five Phytocoris species whose pheromones have been directly (P. californicus, P. relativus, P. difficilis, and P. calli) or indirectly (P. breviusculus) studied are discussed vis-à-vis the pheromone intractable species of Lygus and Lygocoris plant bugs.