Juvenoids cause some insects to form composite cuticles

Metamorphosing insects treated with juvenoids may secrete composite cuticles which combine morphological features of two metamorphic stages within the area secreted by an individual epidermal cell. Characters found combined were pigmentation, tanning, surface sculpturing, and microtrichiae. Neighbouring cells frequently form different types of cuticle. Composite cuticles should not be confused with the more common mosaic cuticles, which are composed of discrete areas with different stage-specific morphology (e.g. some larval patches set in an otherwise normal adult cuticle). Treatment of last instar nymphs of Pyrrhocoris apterus (Hemiptera) with a juvenoid induced secretion of composite cuticle which combined larval morphological features with imaginal pigmentation. Cells remained susceptible to composite cuticle induction over an extended period prior to the actual initiation of cuticle deposition. Composite cuticle which contained larval microtrichiae and pupal tanning were induced with juvenoids in the lepidopterans Hyponomeuta malinella, Hyphantria cunea, Spodoptera littoralis, Mamestra brassicae, Pieris brassicae, Aglais urticae, but not in Galleria mellonella. Composite cuticle possessing both pupal and imaginal morphological features was produced with juvenoids in Leptinotarsa decemlineata (Coleoptera). It is suggested that this type of cuticle reveals the secretory capacities of a single epidermal cell when the cellular reprogramming from one developmental stage to the next has been stabilized at an intermediate point by juvenoids.