Learning of multi-modal stimuli in hawkmoths.

The hawkmoth, Manduca sexta, uses both colour and odour to find flowers when foraging for nectar. In the present study we investigated how vision and olfaction interact during learning. Manduca sexta were equally attracted to a scented blue coloured feeding target (multimodal stimulus) as to one that does not carry any scent (unimodal stimulus; visual) or to an invisible scented target (unimodal stimulus; odour). This naive attraction to multimodal as well as to unimodal stimuli could be manipulated through training. Moths trained to feed from a blue, scented multimodal feeding target will, when tested in a set-up containing all three feeding targets, select the multimodal target as well as the scented, unimodal target, but ignore the visual target. Interestingly, moths trained to feed from a blue, unimodal visual feeding target will select the visual target as well as the scented, multimodal target, but ignore the unimodal odour target. Our results indicate that a multimodal target is perceived as two separate modalities, colour and odour, rather than as a unique fused target. These findings differ from earlier studies of desert ants that perceive combined visual and odour signals as a unique fused stimulus following learning trials.