ULTRASTRUCTURE OF CERATITIS-CAPITATA WIEDEMANN LARVAL INTEGUMENT AND CHANGES INDUCED BY THE IGI CYROMAZINE

Cyromazine inhibits larval growth and mobility and decreases the pupat ion and adult emergence rates in Ceratitis capitata Wiedemann. This wo rk details changes induced by cyromazine in the integument and muscles of third-instar larvae. Severely affected larvae show a conspicuous s welling of the integument in the anterior region of the body, with a l ocal thinness of the cuticle due to the gap between the epicuticle and the procuticle. In other areas, a discontinuity between procuticular layers with many empty spaces, inclusion bodies, and an abnormal thick ening of the cuticle is also observed. The epidermic layer is folded a nd disorganized and its cells have elongated to invade the adjacent sp ace. The epicuticle is the only layer unaffected by the treatment. Mus cle attachments to the cuticle are not broken, but a great inhibition of locomotion is detected and no popped pupae are recorded. However, u nder the electron microscope, muscles with altered mitochondria, disto rted area of fiber arrangement, and a less fiber packing can be observ ed and may account for the lack of movement. Ultrastructural observati ons confirm the hypothesis that cyromazine acts at the hormonal level, as previously stated, but its effects on skeletal muscles are also in dicative of protein involvement in the mode of action of this product, and warrant further investigation. (C) 1994 Academic Press, Inc.