Environmental and hormonal control of body-color polyphenism in Patanga japonica (Orthoptera, Acrididae): Effects of substrate color, crowding, temperature and [His7]-corazonin injection

Abstract

Patanga japonica (Bolívar) shows various body colors in the field. Most nymphs are green in the summer, but some develop non-green colors, such as yellow, white, brown, reddish, and black, in the fall. Nymphs individually reared in white, yellow-green, and black containers showed green, light-green, white, and reddish body colors, and the substrate color significantly influenced the proportions of green nymphs. A few individuals developed black spots and patterns, and such individuals were most frequently observed in the black containers. Nymphs with distinct black patterns were observed when reared in a group of five individuals per container, and the proportion of such individuals varied slightly depending on the brightness of the substrate color. Singly kept nymphs that were allowed to see five other nymphs in another container turned darker than those that were only allowed to see an empty container, suggesting that visual stimuli without mechanical stimulation induced black patterns. In outdoor cages, nymphs tended to develop more pronounced black patterns during their last instar when the hatching date was delayed and the temperature during the later stages of development was decreased. The effect of temperature during the late stadia was tested by transferring a group of third-stadium nymphs from outdoor cool conditions to a high temperature, while other nymphs were continuously maintained outdoors. Markedly melanized individuals were observed in the outdoor cage, whereas the appearance of such individuals was strongly suppressed at a high temperature. Green nymphs injected with synthetic [His7]-corazonin developed black patterns after ecdysis to the following instars and to the adult stage, and some looked indistinguishable in body color from group-reared nymphs. Nymphs injected with this hormone developed black patterns even at a high temperature. Adults looked similar in body coloration with some variation. Their hindwings turned reddish after overwintering. These results demonstrate that P. japonica exhibits body-color pholyphenism.