The use of visual cues in sexual and species discrimination by males of the small sulphur butterfly Eurema lisa (lepidoptera, pieridae)

1. Male Eurema lisa butterflies have specialized scales on the dorsal wing surfaces which selectively and directionally reflect ultraviolet light via an interference phenomenon. Females lack such scales. 2. When perched and approached by another butterfly, individuals of both sexes may open and close the wings several times in rapid succession. This behavior, previously observed in other pierids, has been called the "flutter response". E. lisa males contact and attempt to copulate with females whether or not they perform the flutter response. Fluttering males are ignored. 3. The flutter response has the spatial characteristics necessary to display the male's directional ultraviolet reflectance. Temporal differences between the flutter responses of males and females are small. 4. A two-choice discrimination assay in which static butterflies were presented to caged males demonstrated that E. lisa males can distinguish females from conspecific males solely on the basis of ultraviolet reflectance. 5. Ventral wing coloration and presence or absence of a wing bar effects the attractiveness of a butterfly to E. lisa males. A scheme is suggested by which a male E. lisa distinguishes conspecific females from males and females of two similar and sympatric species.