The effective number of pheromone traps used per feddan to keep the cotton leafworm SJittoralis infestation below its economic inju‌ry level was conducted using three rates of traps; one, two, and three traps/feddan for two successive seasons 1996 and 1997 in three Gov‌ernorates; Sharkia, Menoufyia and Fayoum. Results could be summarized in the following: 1.In most cases there is a positive relationship between numbers of captured male moths and the numbers of pheromone traps set up in cotton fields. 2.The rate of 3 traps/feddan was significantly preferred than in the two other rates. 3.No significant relationship was found between population of egg-masses in cotton fields and numbers of attracted male moths. 4.Pheromone traps caused a decrease in hatchability percent of egg-masses. Rate of reduction was somewhat low in case of the high population of adult moths. 5.Pheromone traps cannot be used alone in controlling this insect on cotton in case of sever infestation, but it could be used within I.P.M. programme to apply insecticides in the suitable time.