Under laboratory condition, one day old eggs 0f laboratory strain of Pectinophora gossypiella (saund) were treated with LC₅₀ values of lufenuron and diflubenzuron, 6.489 and 67.36ppm respectively to study their effects on percentage of hatchability and duration of subsequent larval, pupal, immature stages and longevity, fecundity and fertility of resulted adults. The obtained results clear that the percentage of hatchability of treated eggs were 51.9 and 54% for the two tested compounds, respectively oppose to 95% in untreated control. The incubation period estimated by 6.9 and 6.1 days / lufenuron and diflubenzuron; while in control it recorded 3.2 days. Also, the larval period prolonged to 20.7and 24.6 days in contrary it recorded 15.3 days in control; the pupal period estimated, respectively in treatments and control, by 11.3,13.2 and 7.9 days. On the other hand, the adult stage resulted from treated eggs was highly affected by the used two tested compounds. The respective fecundity reduced to 198.3 and 175.6 eggs/♀ compare to 238.6 eggs/♀ in control. The percentage of hatchability were 60.3 & 59.7 %, respectively compared with 89.3 % in control. Keywords: Pectinophora gossypiella, (PBW), Toxicity , LC50 , Biological studies