Abstract: The body colour variation in cotton aphids (Aphis gossypi) of the natural population developed from zygotes on different host plants and of the population raised from aphids reared individually in the laboratory were investigated. Results showed that the body colour of the aphids would remain unchanged as the new-born aphids during their whole Ide within each generation whatever the populations, the individuals, the hosts and the nutritional conditions may be. But among the successive generations,the body colour changed gradually from green to yellow with rising temperature and from yellow to green with decreasing temperature. X² test demonstrated that there was no correlation between the body colour variation and the nutrients, the host plant, the light and the culturing condition. The variation only correlated to temperature. This is in accord with the phenomenon that under different environmental con dititms the same genotype expresses differently to give rise body colour polymorphism. However, a few dark yellow colour aphids found on the host plant Hibiscus syriacus dis played no change in colour with temperature during their development and transformation to migratory form. It seems there exists a genetic polymorphism of body colour among the aphids. This was proved by the results of observation on embryo development and analysis of karyotype of the insect.

Key words: Aphis gossypii——ecological genetics——genetic polymorphism——reac- tioa norm