The   present research focuses on the effect of teflubenzuron on the 4^th   larval instar of the cotton leafworm, Spodoptera littoralis under   laboratory conditions. Teflubenzuron exhibited larvicidal activity (LC₅₀   8.45 ppm) after 72 hours of treatment. Scanning electron microscopy (SEM)   showed growth disruption and abnormalities in the external morphological   features of cuticle and head capsule in larvae treated with teflubenzuron.   Marked biochemical changes in chitin synthesis pathway were recorded.   Protease enzyme activity was significantly reduced, whereas the activities of   both chitinase and phenoloxidase were significantly elevated in treated   larvae in comparison to controls.