The present investigation aimed to study the effects of some cucumber varieties:- Indian, Japanese and Alpha beta, while squash varieties Holland, Escandarani and Top Kapi on the population density of aphids ,leafhoppers and whitefly insects ,under different potassium fertilization levels(zero,50,100 and 200kg/feddan).The obtained results show pronounced  differences in the population density of the aforementioned   insects on the tested varieties. The least susceptible variety of cucumber was Indian, while the highest susceptible variety was Alpha beta, The least susceptible squash was Holland variety, while the highest susceptible was Top Kapi variety during 2006and 2007 seasons , respectively .The fourth level of potassium fertilization "200kg.potassium sulphate /feddan" recorded the least number of aphids ,leafhoppers and whitefly insects ,while the first level of potassium fertilization "zero kg.potassium sulphate/feddan" increased the aforementioned insects population density . Chemical analysis results showed a negatively relationship between protein, carbohydrate contents and pH values and aphids ,leafhoppers and whitefly infestation in all cucumber and squash varieties. From these results susceptibility of plant variety and potassium fertilization must be considered in the integrated pest management programs as they play very important role in depressing insect population.