SUMMARYLearning plays an important role in food acquisition for a wide range of insects and has been demonstrated to be essential during flower foraging in taxa such as bees, parasitoid wasps, butterflies and moths. However, little attention has been focused on differences in floral cue learning abilities among species and sexes. We examined the associative learning of flower colour with nectar in four butterfly species: Idea leuconoe, Argyreus hyperbius, Pieris rapae and Lycaena phlaeas. All butterflies that were trained learned the flower colours associated with food. The flower colour learning rates were significantly higher in I. leuconoe and A. hyperbius than in P. rapae and L. phlaeas. Among the four species examined, the larger and longer-lived species exhibited higher learning rates. Furthermore, female butterflies showed a significantly higher learning rate than males. This study provides the first evidence that learning abilities related to floral cues differ among butterfly species. The adaptive significance of superior learning abilities in the larger and longer-lived butterfly species and in females is discussed.Key words: associative learning, forewing length, innate colour preference, Lepidoptera, lifespan. THE JOURNAL OF EXPERIMENTAL BIOLOGY3811 Learning rate differences in butterflies Idea leuconoe (Butler) (Danaidae)We used laboratory-reared individuals from the Itami City Museum of Insects, Itami, Osaka, Japan. Butterflies were originally collected in Ishikawa, Uruma, Okinawa, Japan. One to three larvae were reared in a 500ml or 860ml transparent plastic cup on fresh leaves of Parsonia alboflavescens (Dennstedt) Mabberley at 22-25°C and 15h:9h L:D in an incubation room. Argyreus hyperbius hyperbius (Linnaeus) (Nymphalidae)Adult females and larvae were obtained near the Nara campus of Kinki University, Nakamachi, Nara, Japan, from July to August 2004. Adult females were then allowed to oviposit eggs. About 10 larvae were reared together on fresh leaves of several Viola species in 450ml transparent plastic cups at room temperature (range of daily mean: 24-30°C) and natural daylength (range: 14h:10h L:D to 15.5h:8.5h L:D) within the laboratory. Pieris rapae crucivora (Boisduval) (Pieridae)Adult females and larvae ware collected near the Nara campus of Kinki University from September to October 2004. Adult females oviposited eggs, and the larvae were reared on fresh leaves of Brassica oleracea L. and Raphanus sativus L. in 450ml transparent plastic cups (10 larvae per cup) at room temperature (14-29°C) and natural daylength (12h:12h L:D to 14h:10h L:D) within the laboratory.

Learning plays an important role in food acquisition for a wide range of insects. To increase their foraging efficiency, flower-visiting insects may learn to associate floral cues with the presence (so-called reward learning) or the absence (so-called non-reward learning) of a reward. Reward learning whilst foraging for flowers has been demonstrated in many insect taxa, whilst non-reward learning in flower-visiting insects has been demonstrated only in honeybees, bumblebees and hawkmoths. This study examined both reward and non-reward learning abilities in the butterfly Byasa alcinous whilst foraging among artificial flowers of different colours. This butterfly showed both types of learning, although butterflies of both sexes learned faster via reward learning. In addition, females learned via reward learning faster than males. To the best of our knowledge, these are the first empirical data on the learning speed of both reward and non-reward learning in insects. We discuss the adaptive significance of a lower learning speed for non-reward learning when foraging on flowers.