Phase Variation in non-swarming Grasshoppers

Abstract

1. All the species of Siberian grasshoppers that have been studied in sufficient detail consist of a series of races exhibiting parallel coloration, structure and behaviour characters.2. Every race ofChorthippus albomarginatus, Zett.,Aeropus sibiricus, L., and of other species, has in its hopper and adult stage a series of colour forms analogous in their characters to the phasessolitaria, transiensandgregariaof swarming locusts.3. These colour forms are very unstable and undergo changes during the individual life due to the conditions of breeding.4. Breeding in crowded conditions results in the predominance of dark-coloured forms, with black and sometimes with orange spots. Breeding in isolation, on the contrary, results in light forms of various colours.5. No complete transformation of all the individuals in a population is observed in Siberian grasshoppers, and the intermediate forms represent a considerable portion of every population.6. These colour forms, which can be considered as phases, differ also in their structural characters. Phasegregariais larger and more long-winged than phasesolitaria.7. The phases differ further in their behaviour, ph.gregariabeing more mobile and inclined to migrations, than ph.solitaria.8. Every species and every race which have been studied exhibit a potential ability to produce phases, but this ability is not equal in all species and races. Those species and races which, owing to their habits and to the conditions of their habitats, can multiply in masses in restricted areas are more inclined to phase variability.