Ultrastructure of Ceratitis capitata Wiedemann Larval Integument and Changes Induced by the IGI Cyromazine

Abstract

Cyromazine inhibits larval growth and mobility and decreases the pupation and adult emergence rates in Ceratitis capitata Wiedemann. This work details changes induced by cyromazine in the integument and muscles of third-instar larvae. Severely affected larvae show a conspicuous swelling of the integument in the anterior region of the body, with a local 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 thickening of the cuticle is also observed. The epidermic layer is folded and disorganized and its cells have elongated to invade the adjacent space. The epicuticle is the only layer unaffected by the treatment. Muscle attachments to the cuticle are not broken, but a great inhibition of locomotion is detected and no popped pupae are recorded. However, under the electron microscope, muscles with altered mitochondria, distorted area of fiber arrangement, and a less fiber packing can be observed and may account for the lack of movement. Ultrastructural observations confirm the hypothesis that cyromazine acts at the hormonal level, as previously stated, but its effects on skeletal muscles are also indicative of protein involvement in the mode of action of this product, and warrant further investigation.