CNRS, Laboratoire de Neurobiologie, Communication chimique, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
In insect species, the antennal nerve with all sensory neuron axons is connected directly to two antennal lobes. These lobes which contain glomeruli, form the first-order olfactory center in the deutocerebrum. The macroglomerular complex observed in males of many insect species has been implicated in perception of female sex pheromone. Unlike other species, reproductive activity in N. cinerea involves pheromone production by males and perception by females. Males produce two pheromones, i.e. one for long-distance attraction and another for induction of copulation (aphrodisiac). The main components of both pheromones are acetoin, 2-methylthiazolidine and 4-ethyl-2-methoxyphenol. The purpose of this study was to compare the neuroanatomy of the antennal lobes (deutocerebrum) in male and female N. cinerea and determine the role of right and left female antenna in perception of male sex pheromones. We compared deutocerebrum of 5 females and 5 males. No macroglomerular complex was found in either sex. Conversely a sex-related difference was observed in the number of glomeruli in the right and left deutocerebrum. Unlike males which usually presented the same number of glomeruli on each side, females presented more glomeruli on the right than left. To ascertain the functional consequences of this difference, behavioral experiments were carried out to compare the outcome of mating after removal of one antenna. Results showed a higher success rate for females with intact right antenna than females with intact left antenna. These results suggest that the right antenna in association with a higher number of olfactory glomeruli in the right deutocerebrum plays a predominant role in the perception of male sex pheromones by female cockroaches.