Cellular patterns and spectral sensitivity of larval ocelli in the swallowtail butterflyPapilio

Summary

Caterpillars of the swallowtail butterflyPapilio xuthus L. like most lepidopterans have six larval ocelli (stemmata) on each side of the head (Fig. 1). Five of these (II–VI) are arranged in a close ellipsoidal cluster from which number I is somewhat isolated ventrally (Fig. 2). Each stemma has seven retinular cells (R) organized in two tiers (proximal and distal, Fig. 3) but the cellular patterns and spectral sensitivities fall into three classes. As proved by intracellular recordings (Fig. 4) stemmata I and III have five green receptors (λmax ca. 530 nm) and two blue ones (λmax ca. 450 nm) (Fig. 5). The other ocelli have only four green and one blue cell, but have in addition two UV units each (λmax ca. 370 nm); in II and IV one green cell (R6) is proximally located (Fig. 6), in V and VI it is distal. All distal cells whether three (I–IV) or four (V, VI) in number are green units. Hence all blue and UV receptors are in the proximal cell tier with UV limited to R5 and R7, blue to R4, R5, and R7 (Fig. 7).