Environmentally Induced Color Dimorphisms in Grasshoppers. Syrbula admirabilis, Dichromorpha viridis, and Chortophaga viridifasciata1

Abstract

The grasshoppers Syrbula admirabilis (Uhler), Chortophaga viridifasciata (De Geer), and Dichromorpha viridis (Scudder) (Orthoptera: Acrididae) occur in 2 color phases in the field; individuals either have extensive green areas (green morphs) or lack green entirely (brown morphs). In nature, males and females are green or brown in the nymphal stages; however, in S. admirabilis and C. viridifasciata green adult males are rare. Green morphs are more frequent in green habitats and brown morphs are more abundant in dry, brown habitats. The frequency of green morphs at a given locality increases and that of brown morphs declines when the habitat becomes greener. The opposite shift occurs as the habitat dries up. Fresh grass and high humidities favor the retention of green pigmentation in Syrbula and low humidities and dry grass result in color changes from green to brown within 2 weeks, or the retention of brown pigmentation. These results suggest that color changes are causally related to water uptake and water loss in this species. Chortophaga nymphs tended to turn brown under all laboratory conditions. Changes in the color of the background produced no significant changes in color of the insects. Observations in the field suggest that the tendency to remain motionless is greater in species which more closely resemble the vegetation background color.