Flight behaviour of the hawkmoth Manduca sexta towards unimodal and multimodal targets.

Here, we analyse the flight behaviour of the hawkmoth Manduca sexta while it approaches three different artificial flower stimuli: a clearly visible blue flower, an invisible scented flower and a flower that is both visible and scented. By tracking the moths in fine temporal detail, we find that flight towards an artificial flower differs depending on whether the stimulus is unimodal (either visual or olfactory) or multimodal (both visual and olfactory). In all three cases, the moth reduces its speed as it nears the target but the speed is higher overall when the visual stimulus is not present. Visual feedback, as well as the concentration gradient of the odour, is used to guide the moths towards the stimulus. The main difference in flight behaviour between an approach towards a visual and a multimodal stimulus is that the olfactory information makes the moths turn more rapidly towards the multimodal stimulus. We also find that moths extend their proboscises in front of a clearly visible feeder independent of whether an odour is present. In contrast, a scented transparent artificial flower only occasionally triggers this response.