Synergy between visual and olfactory cues in nectar feeding by na.ve hawkmoths, Manduca sexta

Communication between flowering plants and their pollinators involves innate, learned and deceptive sensory signals. Nocturnal, hawkmoth-pollinated flowers are among the most reflective and strongly scented known, suggesting the potential for multimodal sensory communication with pollinators. We measured the relative importance of these overstated signals, both alone and in combination, to nectar feeding by naïve male hawkmoths, Manduca sexta. In the absence of fragrance, moths hovered and repeatedly passed (in flight) within 1 m above arrays of model paper flowers. The presence of plant odours elicited significantly more hovers and close passes, as well as three additional behaviours: approaches to the paper flowers, approaches to the hidden odour source and nectar feeding. However, approaches to odour sources never resulted in proboscis extension or probing in the absence of a visual target. Nectar feeding increased six-fold when paper and natural flowers were presented in mixed arrays, but moths did not show preferential visits or constancy to either type of flower. Significantly ordered behavioural sequences were observed when both visual and olfactory stimuli were present, but not when fragrance was absent. The largest conditional probabilities indicated a chain of responses beginning with hovering and leading to floral approach and nectar feeding. As single modality cues, both floral fragrance and visual display are innately attractive to male M. sexta, but the combination thereof is required to elicit proboscis extension and feeding.