Multi-component sex pheromone processing in the American cockroach: comparative aspects across insects from molecules...

Because of its heavy reliance on chemical senses in guiding behavioral choices, the American cockroach Periplaneta americana is a valuable animal model for understanding the neural basis of olfactory behavior. In this Review, we summarize recent advances in research on sex pheromone detection and processing in P. americana, a walking insect, and compare its characteristic features with those of flying moths. Insects generally utilize multi-component sex pheromones composed of major and minor components. Female P. americana emit sex pheromones composed of the major component periplanone-B (PB) and minor component periplanone-A (PA), and this insect is unique in that the minor pheromone component can either promote or suppress male courtship behavior. PB strongly elicits attraction and courtship behaviors in males, whereas PA alone weakly induces these behaviors at high doses but suppresses PB-induced courtship behaviors when presented together with PB. Here, we describe current knowledge on the neural processing of PA and PB in the cockroach from the receptors to courtship behaviors. First, we summarize the functional properties of periplanone receptor genes and propose a nomenclature for them. We then discuss recent advances in the neural control of courtship behavior via PA- and PB-processing pathways, from the periphery to higher brain centers. In particular, interactions between pathways for processing major and minor components enable PA to exert both facilitatory and inhibitory effects on the PB-processing pathway. Finally, we argue that such interactions might provide the neural basis for a walking-orientation strategy as males approach the pheromone source.