Cotton aphid,\%Aphis gossyipii\% is found on various plants with universal distribution.It causes serious damage on cotton and vegetable in China,especially in northwest droughty or semi-droughty areas.The population of cotton aphid differentiates obviously in types.On cotton,the population density usually have two peak periods.One occurs in spring with green or yellowish green body colour,infests the top tender leaves,it is usually called as seedling type;the other is in summer in blight yellow colour and ...