The larvae of Pieris rapae L. topically treated with acetone extracts of the leaves of Tephrosia vogelii Hook f. or rotenone developed into the malformed larvae and pupae. The ultra structure of the integument of the malformed larvae and pupae were observed. It was found that the deformation caused by rotenone and its analogs mainly resulted from the influences of decomposition of the old cuticle and synthesis of new cuticle. Significant differences in content of the chitin, total fats and total proteins between the treatment and control occurred.