| Spodoptera frugiperda (J. E. Smith), considered for a long time a generalist feeder, now is known to comprise two genetically differentiated host-associated strains, designated as corn strain (CS) and rice strain (RS). Previous studies have revealed that females attract males of both strains but mate almost exclusively with their own strain. Males are known to possess two sets of hairpencils (potential pheromone-producing structures), but their role has not been previously assessed. The species is a good model to test Phelan's (1992) Asymmetric Tracking model, which predicts that the sex with the greater parental investment will be more discriminating in their response to sexual signals, and that signals produced by the other sex will evolve to track this preference. Courtship sequences of S. frugiperda were videorecorded in an arena under infrared light, and analyzed frame by frame. Individual behaviors were transcribed to three-dimension transitional matrices, which were submitted to Information Theory analysis for quantification of intra- and inter-individual communication.; Information analysis confirmed the existence of an asymmetry in the response between the sexes in S. frugiperda. In both intra- and inter-strain courtships, female-to-ale information flow was lower than for male-to-female. Moreover, both RS and CS females were more likely to show a receptive response to male behaviors associated with hairpencil displays when courted by males of their own strain. These findings of a male-signal-based female preference for assortative mating, particularly in the absence of mate discrimination by males are consistent with the predictions of the Asymmetric Tracking hypothesis (Phelan, 1992) and the more specific hypothesis of Phelan and Baker (1987) that many lepidopteran male pheromones may have evolved in the context of reproductive isolation through sexual selection.; Chemical characterization of each set of hairpencils was also conducted by solvent extraction and analysis by gas chromatography/mass spectrometry. Among the ca. 150 chemicals identified in the extracts, two stood out as showing clear differences between males of the two strains, 2,4-diphenyl-4-methyl-l-(E)-pentene and 2,4-diphenyl-4-methyl-2-(Z)-pentene. These compounds had not previously been described in any Lepidoptera. |
