Permanent larva phenomenon is the elongation in the larval stage. This phenomenon occurs as a result of imbalance in insect hormones after treating the larvae with some insecticides such as insect growth regulators (IGR). This work aimed to explain this phenomenon as a result of treating S. littoralis 4^th instar larvae with Spinetoram, Lambda-cyhalothrin, Chlorpyrifos and Emamectin Benzoate. Highly significant increase in larval duration was recorded in treated larva. Significant changes in total carbohydrates, total protein and total lipid contents as well as the main enzymes activities were recorded in the permanent larvae. Genetic differences between normal untreated S. littoralis and permanent larvae were also studied.