Chemical communication in the German cockroach: Pheromones and heterospecific courtship eliciting compounds

Contact sex pheromones are vital for reproductive success in many species, yet little is known about their structural identity and regulation. An exception for this rule is the German cockroach, Blattella germanica, whose contact sex pheromone has been extensively studied in relation to regulation. Here we describe findings of studies relating to structure-activity relationship.;We show that contrary to expectation, the naturally occurring stereoisomer of the pheromone is the least active of the four possible stereoisomers, and discuss the possible reasons for that. Extensive behavioral assays with synthetic pheromone analogs and the natural pheromone were conducted to validate this result. Next we report the finding of two additional pheromone components, predicted from prior knowledge of biosynthetic pathway, and confirmation of their behavioral activity with synthetic analogs. Various separation techniques, such as flash chromatography, high performance liquid chromatography and gas chromatography coupled with mass spectrometry, guided by behavioral assays, were used for this end.;Through our studies, two intriguing phenomena were revealed: the German cockroach male courts immature stages of its own species, and members of five other cockroach species. The above mentioned techniques were used to identify the compounds responsible for eliciting courtship in nymphs and other species. The results show that last instar female nymphs share common pheromonal components with adult female contact sex pheromone, which coincides with other sexual differentiation events that occur in the last instar stage. Young nymphs and last instar female nymphs elicit courtship through a different, yet to be identified compound, or set of compounds. This may be a case of sexual mimicry with a potential adaptive value, such as avoiding aggression or gaining nutritional benefits. The courtship eliciting compounds in one of the other cockroach species, Blatta orientalis, were identified as different from any of the sex pheromone components of B. germanica, yet they share common features. This suggests that the German cockroach male responds to a broader range of chemical structures than necessary for sexual and species recognition. Possible causes for this broad tuning phenomenon are discussed.