The learning abilities of the white cabbage butterfly, Pieris rapae , foraging for flowers

This study examines the role of learning and memory in the butterfly Pieris rapae crucivora Boisduval during foraging for flowers. In an outdoor cage with 6 flower species, P. rapae showed various visiting patterns: some visited only one species, while others visited several species in a day. The foraging process for flowers of Erigeron annuus (L.) Pers. could be divided into two successive steps: (1) landing on the nectaring caputs, and (2) finding the source of nectar in the caput. Butterflies learned to proceed through the two steps more efficiently with successive attempts: they gradually decreased landings on nectarless caputs and probings on the nectarless petals of ligulate flowers respectively. As a result, handling time per unit caputs became shorter, and apparent rewards per unit time, i.e. the efficiency of collecting nectar, increased. In addition, once learned, P. rapae could remember a rewarding flower color for 3 days, which was not interfered with by learning another flower color. This indicates that P. rapae keeps memory for a period longer than 3 days, and that they can remember at least two flower species as suitable flower resources. Furthermore, data indicated that they sometimes can apply the foraging skills obtained on other flower species to a novel one. These abilities could enable butterflies to easily switch flower species, or to enhance labile preference. It has been known that P. rapae also shows flower constancy, which may be due to memory constraints. Therefore, they may appropriately use two foraging tactics: visit consistency and labile preference, to get enough nectar according to their circumstances.