DIFFERENCES IN SEX-PHEROMONE COMMUNICATION-SYSTEMS OF CLOSELY-RELATEDSPECIES - SPODOPTERA LATIFASCIA (WALKER) AND S-DESCOINSI LALANNECASSOU AND SILVAIN (LEPIDOPTERA, NOCTUIDAE)

S. latifascia and S. descoinsi are closely related species that occur sympatrically over limited areas in French Guiana. We examined allopat ric populations, S. latifascia originating from Barbados and S. descoi nsi from French Guiana. Studies on nocturnal activity cycles showed te mporal partitioning of female calling behavior, male sexual activity, and mating behavior. S. descoinsi were sexually active in the first ha lf of the scotophase whereas S. latifascia were sexually active in the second half. Seven compounds (Z9-14: Ac, Z9,E12-14: Ac, Z11-16: Ac, E 9,E12-14: Ac, Z9-14: Aid, Z9,E11-14:Ac and Z11-14:Ac) were identified in females of both S. latifascia and S. descoinsi extracts. Z9-14:Ac w as a main pheromone component for the two species. The major differenc e between the pheromones of S. latifascia and S. descoinsi was the pro portion of Z9,E12-14:Ac in the extracts: 7% for S. latifascia and 42% for S. descoinsi. The proportion of Z9,E12-14:Ac relative to the sum o f Z9-14:Ac and Z9,E12-14:Ac in individual gland extracts was 4 +/- 1% (mean +/- standard deviation) for S. latifascia and 44.8 +/- 6% for S. descoinsi. Electrophysiological studies showed no major differences b etween species in the morphology and physiology of the pheromone recep tors of males. Receptors were identified for Z9-14:Ac and Z9,E12-14:Ac , but no receptor was found for the other compounds. In the wind tunne l, synthetic blends with Z9-14:Ac and Z9,E12-14:Ac gave the same behav ioral responses as conspecific female extracts for the males of the tw o species. Some cross-attraction was observed with synthetic blends an d female extracts. Nethertheless, previous field trapping experiments in French Guiana were species-specific and suggested differences in th e attractivity of males. In the laboratory, S. latifascia and S. desco insi could hybridize in both reciprocal crosses. Female S. descoinsi x male S. latifascia mating rate was significantly lower than for the r eciprocal cross, and 26.7% of female S. descoinsi could not separate f rom male S. latifascia after mating. These copulatory problems may inv olve genital incompatibilities between males and females. Several barr iers against interbreeding between S. latifascia and S. descoinsi seem to combine including differences in nocturnal activity cycles, pherom one differences; and genital barriers. The study of sympatric populati ons will be necessary to define the role of sex pheromones in the repr oductive isolation of S. latifascia and S. descoinsi.