Male scent-producing structures in Colias butterflies - Function, localization, and adaptive features

During successful courtship in sulfur butterflies, virgin females respond to males by assuming a stationary posture and extending the abdomen ventrally from between the hindwings, thereby permitting copulation. In the clouded sulfur, Colias philodice Godard, this response was used in a laboratory bioassay to confirm the existence of a male chemical signal demonstrated by a previous worker and to document the signal's behavioral function and source. The male scent is shown to be required, in part, to reliably elicit abdominal extension and to be emitted from a patch of cells and scales associated with the dorsal surface of the male hind wing near the wing base. Experiments also show that evaporation of the signal is reduced when the source is covered by the forewing as it is at rest and in flight. These data, coupled with other information on male chemical signals in sulfur butterflies and other Lepidoptera, suggest that in sulfurs the morphology and chemistry of the scent glands along with the behavior of the male are structured in a way that minimizes the evaporative loss of scent from the wings when the male is not courting females.