The Relative Importance of Flower Color and Shape for the Foraging Monarch Butterfly (Lepidoptera: Nymphalidae)

Flowers attract and guide pollinators via a wide array of sensory stimuli, including colors, odors, textures, and even sounds. Bees are known to respond to and learn multimodal and multicomponent floral cues, whereas, historically, studies of learning in butterflies have focused on a single visual stimulus component, most often color. In this study, we examine whether Monarch butterflies (Danaus plexippus L.) can learn to associate a compound visual stimulus, i.e., color and shape together, with a nectar reward. We also examine the relative importance of color and shape as cues for foraging butterflies. Our results indicate that within the visual modality, foraging Monarchs learn color more readily than shape. Monarchs, however, are capable of learning to associate shape with a sugar reward independent of color, and they may also be capable of learning the compound stimulus of color and shape in the context of foraging. We suggest that the hierarchical importance of cues is likely to vary depending on ecological context, and that although color may be most relevant for a nectar-foraging butterfly, shape may be a more useful cue for a butterfly searching for an oviposition substrate.