The current work was carried out to evaluate the biochemical effects of LC 50 of four compounds; emamectin and spinetoram as bioinsecticides, hexaflumuron and teflubenzuron as Insect growth regulators (IGR's) against

Laboratory studies were carried out to investigate the efficacy of the chitin synthesis inhibitor (cyromazine) against all larval stages of Culex pipiens. The compound was tested its efficacy on larval mortality, larval duration, pupation, pupal duration and adult emergence. Also, the histological effects of cyromazine on the midgut, the integument, the fatbodies and the muscles of 4 th larval instar treated as 1 st larval instar were studied. The tested compound increased the larval mortality, decreased the percent pupation and adult emergence and prolonged the pupal duration. Also, this compound elicited histological effects on the midgut, the integument, the fat bodies and the muscles of 4 th larval instar of C. pipiens treated as 1 st larval instar with 0.01 and 0.1 ppm.