BIOSYSTEMATICS OF THE GENUS EUXOA (LEPIDOPTERA: NOCTUIDAE) XV. SEX PHEROMONE CROSS ATTRACTANCY AMONG THE THREE CLOSELY RELATED SPECIES OF THE DECLARATA GROUP

Male release-recapture experiments show that under natural photoperiod there is no cross attractancy between species of the sympatric pairs E. declarata and E. campestris or E. declarata and E. rockburnei, but that there is between the parapatric pair, E. campestris and E. rockburnei. When the calling periods of E. declarata and E. campestris females are synchronized by photoperiod manipulation there is cross attraction between these two species as well. However, in mating discrimination tests between E. declarata and E. campestris the normally strong bias against interspecific mating is only partially overcome by synchronizing mating activity rhythms. The residual tendency for conspecific mating is more likely due to imperfect synchronization of mating rhythms or differences in close range courtship behavior than to differences in attraction pheromone. Males of all three species are attracted to the same synthetic attractants. The results are consistent with the hypothesis that the attraction pheromones of the three species in the declarata group are very similar and are unlikely to play a major role in reproductive isolation, which is probably effected primarily by differences in circadian rhythms of mating activity.