Role of Larval Stemmata in Control of Pupal Color and Pupation Site Preference in Swallowtail Butterflies <I>Papilio troilus</I>, <I>Papilio polyxenes</I>, <I>Eurytides marcellus</I>, and <I>Papilio glaucus</I> (Lepidoptera: Papilionidae)

Abstract

Swallowtail butterfly species (Lepidoptera: Papilionidae) dimorphic for pupal color produce cryptic brown and green pupae in response to environmental cues. The occurrence of perceptible and reliable cues about pupation site color is a necessary condition for the evolution of this adaptation. By comparing the pupal color responses of prepupal larvae blinded by cautery of the stemmata with prepupal larvae cauterized, but not blinded, we show that the larval eyes (stemmata) mediate the pupal color response. Using a similar comparison, we also show that the stemmata are involved in pupation site choice by prepupal larvae. Considered in light of previously published work on the spectral sensitivities of stemmatal photoreceptors, the absorption spectra of green vegetation and the effects of different colored surfaces on pupal color, our results suggest a model for the proximate control of pupal color involving the differential stimulation of green and blue stemmatal photoreceptors.