A hawkmoth's point of view - Innate symmetry preferences are informed by floral display and foraging function in an insect pollinator

Abstract

Floral visual cues are key for flower recognition and feeding in many pollinators. In insects, innate preferences for characteristic floral colour and pattern cues can guide naive foragers during their initial foraging. Symmetry is suggested to be one such foraging cue, since it is a remarkably conserved floral feature, with flowers mainly displaying radial or bilateral morphologies. Insect pollinators like honeybees, bumblebees, and hoverflies have been found to distinguish symmetry from asymmetry spontaneously or through learning. However, whether innate preferences for floral symmetry types, i.e. radial or bilateral, influence naive flower choice, and whether such preferences are linked to functional benefits during foraging remains uncertain.We investigated innate symmetry choice and its associated foraging function in the hummingbird hawkmoth (Macroglossum stellatarum). Besides relying on pattern cues for flower choice, these hawkmoths feed while hovering, making symmetry a valuable visual cue for flight and proboscis control. In choice assays, the hawkmoths' innate preferences for symmetry types depended on the floral display planes, with considerable differences between the horizontal and vertical displays. Tracking the hawkmoths during foraging revealed that in both display planes, the innately preferred patterns increased foraging success by guiding approach and nectary search. While an analysis of flowers visited by hawkmoths in nature did not reveal the same link between symmetry and display plane, a majority of plant species with vertically displayed flowers showed features matching those innately preferred by the hawkmoths. In this study, we provide the first instance of display-dependent innate foraging preferences and highlight how visuomotor strategies in nectivorous insects may have coevolved with flower features.