Pupal Warning Coloration of Three Species of Cystidia (Lepidoptera: Geometridae: Ennominae) in Relation to Their Pupation Sites

SIMPLE SUMMARY: The evolution of warning (aposematic) colors in insects has been well studied for adult wings and larval bodies. However, there are few reports on the evolution of warning colors in pupae. We hypothesized that pupal coloration of the moth Cystidia (Geometridae: Ennominae) is aposematic, and examined the color pattern, pupation site, palatability, and predator’s learning for three species of Cystidia. Pupae of C. couaggaria and C. truncangulata have a yellow surface dotted with black spots, that seems conspicuous for the visually food-searching predators. These two species make the naked pupae on the surface of branches and leaves above the ground, where they are more conspicuous against the predators. Pupae of C. stratonice also have a yellow surface with black spots, but the head, thorax, wing pads, and abdominal end are uniformly blackish. This species also differs from the other two species in that it pupates in an above-ground pouch made of leaves by spinning with course silk. In the predation experiment using lizards as one of the potential predators, pupae of all three species were repelled, and repeated biting of pupae increased the lizard’s tendency to avoid them. These results suggest that the conspicuous coloration of unpalatable pupae of Cystidia may function as a warning color. However, C. stratonice pupating in the leaf pouch may halve the function of the warning color, and the concealing dark color in the pouch may be more developed in this species than in the other two species. ABSTRACT: Many insects display a cryptic color to avoid detection by predators that search for prey by sight. However, some species with chemicals that predators dislike may display a warning color (aposematism) to predators. The predators can learn easier that the species is unsuitable as prey if the color is more conspicuous. Therefore, it is assumed that the acquisition of the warning color requires not only unpalatability, but also exposure of the color to predators and the ability of predators to recognize and learn it unpalatable. In the moths of the subfamily Ennominae, almost all of genera produce uniformly brown or green pupae, but the pupae of the genus Cystidia have conspicuous coloration of yellow background and black spots. In this study, to clarify whether the color of these pupae is the warning color or not, we compared the coloration, pupation site, and palatability among the three species of this genus: C. couaggaria, C. truncangulata, and C. stratonice. Learning by the predators was also examined using lizards as a potential predator of the moths. The results showed that all three species were repelled (unpalatable) by the lizards, and that repeated providing of the pupae to the lizards decreased their willingness to prey on them (probably due to learning). Pupation sites of C. couaggaria and C. truncangulata were located on the surface of branches and leaves high above the ground, whereas C. stratonice pupated in the space of leaves spun with course silk at lower site above the ground. Thus, the conspicuous coloration of pupal Cystidia is considered to be a warning color, but the pupae of C. stratonice are more blackish than those of the most closely related C. truncangulata. The pupal color of C. stratonice is likely to have a dual meaning as cryptic and warning colors. The dark colored pupa may be inconspicuous when hidden within the leaf space, but once detected by the predators, the yellow color of the pupa may function as a warning color.