Abstract: The possible causes of the formation of aphid host biotypes were reviewed. In ecological levels, the formation is mainly related with the selection capacity to host plants, the natural enemies, the symbionts (coexists ) and resistance to insecticides, and so on. The host biotypes have their genetic bases, including the mutation or change in enzymes and chromosomes, sexual reproduction, assortive mating and genetic differentiation of population. But the detailed causes for a certain host biotype in aphids were poorly understood at present.

Key words: Aphid, host biotype, selection capacity, genetic differentiation