The present investigation aimed to study the effects of certain agricultureal practices (eggplant varieties ,Bonica ,Oneta & Balady  and pepper plant varieties ,Orly ,Maor & Marconi )under the effects of different potassium fertilization levels (zero , 50, 100 and 200 kg potassium  sulphate /feddan ), the effect of some chemical contents        (Total protein ,carbohydrate and pH values) on the population density of different leafhopper , aphid and whitefly insects infesting the aforementioned plant varieties were also tested .The  obtained results show pronounced  differences in the population density of these  insects under test as influenced  by eggplant and pepper plant varieties and potassium fertilization rate. Chemical analysis of the used eggplant and pepper plant varieties under different potassium fertilization levels pointed out that the population density of the aforementioned homopterous insects was correlated with the chemical constituents (Total protein ,carbohydrate contents and PH values ) and also with quantity of yield. Therefore, it could be recommended that potassium fertilization along with the most suitable plant variety must be included in the integrated pest management programs.