The insecticidal activities of four insecticides (i.e. synthetic pyrethroid"lambdathrin"; indoxacarb "steward"; mineral oil"masrona" and emamectin benzoate "proclaim") were evaluated on the 1^st instar larvae of the pink bollworm, Pectinophora gossypiella, as well as determining the biochemical changes and histological effects in 10-day treated insects after treatment with LC_50s of aforementioned insecticides. Lambdathrin was the most toxic insecticides followed by proclaim, then steward whereas masrona was the least toxic one. The corresponding LC₅₀values were 1.0097, 4.0423, 300.47, and 69917.34 ppm, respectively. Fluctuated biochemical changes were achieved. Total soluble protein content decreased insignificantly after treatment with lambdathrin, masrona, and proclaim. Otherwise, treatment with steward caused a significant increase in the protein content by 85.5% than control. For total lipids content, steward caused an insignificant decrease in the total lipids content by 44.62%. While lambdathrin and masrona caused a significant decrease by 50.78 and 72.58%, respectively. Also, it is noticeable that proclaim caused a significant increase in the total lipids content by 145.19-fold than control. For the determination of the changes in the AST and ALT activity, lambdathrin caused a significant increase in the AST activity by 99.93% and a significant decrease in the ALT activity by 57.12%. Steward activated both of the AST and ALT activities over control by 308.41 & 151.77%, respectively. Masrona didn't affect AST activity. while it caused a significant decrease in the ALT activity by 64.49%. On the other hand, treatment with proclaimdidn't affect both AST and ALT activity.
         According to histological effects, signs of intoxication have begun on the level of the mid-gut. Treated larvae showed morphologically, malformation, and destruction of the epithelial columnar cells, vacuolization, and sometimes detachment of the basement and peritrophic membranes of the epithelial cells afterlambdathrin, steward, masrona and proclaim treatments. At the level of masrona and steward, treatments exhibited obvious damage to the boundaries of epithelial cells leading to disruption and fusion in the columnar epithelium cells and necrotic epithelium in some regions. On the other hand, larvae treated with both lambdathrin and proclaim produced less damage of the epithelial columnar cells. However, in both masrona and proclaim treatments, microvilli of brush border appeared to be normal.