A COMPARISON OF CUTICLE DEPOSITION DURING THE PREECLOSION AND POSTECLOSION STAGES OF THE ADULT WEEVIL, ANTHONOMUS-GRANDIS BOHEMAN (COLEOPTERA, CURCULIONIDAE)

An ultrastructural analysis of cuticle deposition before and after adult eclosion of the cotton boll weevil, Anthonomus grandis Boheman (Coleoptera : Curculionidae), is made to monitor the intra- and extracellular events that accompany the shift in cuticle architecture. A typical 5-layered epicuticle and a multi-lamellate procuticle are deposited during the pharate adult stage. Secretion of the epicuticle and the procuticle begins about 2 and 4 days after pupation, respectively. Following eclosion, a lattice-like endocuticle is secreted in the form of layers of parallel rod- or beam-shaped macrofibers. Deposition of endocuticle over the first week after emergence, is at a rate of 3 or 4 layers per day. The imaginal endocuticle accounts for the major portion of the cuticle mass as there is about a 14-fold increase in sclerite thickness and an overall 4-fold increase in non KOH-extractable exoskeletal mass during the first week after emergence. Extensive cytoskeletal and surface remodeling plus a change in secretory product packaging occurs at the apical region of the epidermal cells upon shifting to deposition of the endocuticle. Intralayer orientation of the macrofibers is under cellular control and is accomplished by the formation of templates consisting of membrane placque-bearing, canal-like depressions on the apical surface extending across cell borders. Comparisons of cuticle sections to simulated plots drawn via computer graphics, show that each successive layer of macrofibers is rotated with respect to the overlying layer by an angle of about 72-degrees. Except for vertical columns of cuticular fibers that support pore canals, microfibril orientation within the procuticle/exocuticle generally follows the Bouligand model for a typical lamellate arthropod cuticle. Direct cellular control over the interlaminar orientation of the microfibrils forming the procuticle could not be discerned in this study.