Correlations between epidermal cell structure and endogenous hormone titers during the fifth larval instar of the tobacco hornworm, Manduca sexta.

Epidermal cell morphology and cuticle production in Manduca sexta are directly influenced by both ecdysterone and juvenile hormone. Up to day 6 of the last larval instar, post-molt endocuticle is continuously deposited even though cells undergo a partial and temporary separation from the overlying cuticle at the time when a small ecdysteroid peak is detected (approximately day 3.5). At about days 6--7 when another, larger ecdysteroid peak is present, apolysis occurs accompanied by the appearance of edcysial droplets. Following apolysis, layers of pupal cuticle are deposited. Increased quantities of rough endoplasmic reticulum characterize the epidermis at times of peak endocuticle deposition (day 3, larval cuticle; day 9, pupal cuticle). Dense pigment inclusions are found in epidermis from the day of ecdysis to the last larval instar until they are eliminated 5 days later. These dense bodies migrate from cell apex to base in the absence of juvenile hormone (or in the presence of a negligible amount of juvenile hormone) and probably contain insecticyanin.