FLOWER CONSTANCY AND LEARNING IN FORAGING PREFERENCES OF THE GREEN-VEINED WHITE BUTTERFLY PIERIS-NAPI

1. Evolutionary pressure should select for efficient foraging strategi es, within the constraints of other selective forces. We assess the me chanisms underlying flower choice in the butterfly, Pieris napi (L.), which as an adult forages for nectar. Experiments were carried out on a laboratory colony, using artificial flowers of two colours, and repl icated on two successive generations. 2. When nectar was freely availa ble from all flowers, equal numbers of butterflies visited each colour , but individual butterflies exhibited flower constancy, showing a str ong preference for one colour or the other. 3. Following 3 day conditi oning periods in which nectar was available from flowers of one colour only, butterflies responded by developing a preference for this colou r, which persisted when both flower colours were refilled. This prefer ence could subsequently be switched to the other flower colour followi ng a further 3 days of conditioning. These are interpreted as adaptive (learned) responses, which would have obvious selective benefits in t he field, enabling butterflies to avoid flower species which experienc e has shown are poor sources of nectar, and to adapt to temporal and s patial changes in nectar availability.