Technical Abstract: Female Phytocoris sp. 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 shutoff of conspecific male attraction. However, the binary blend of HA and E2OA was only slightly attractive to males, and was significantly less active than the 4-component blend. The two ternary blends, HA/OA/E2OA and HA/E2HA/E2OA, were each as attractive as the full 4-component blend, but removal of both E2HA and OA from the full blend dramatically reduces the attraction of Phytocoris sp. males. Evidence from previous pheromone research on other Phytocoris species suggests that the apparent chemical redundancy in the pheromone of Phytocoris sp. 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. sp.) or indirectly (P. breviusculus) studied are discussed vis-à-vis the as yet unidentified pheromones of intractable species such Lygus and Lygocoris plant bugs.