Introduction: Morphology and Development of the Wing with Scales

Most wings of butterflies and moths, or lepidopterans, are completely covered with a large number of common scales and fringed with marginal scales, which is the main feature specific to most lepidopteran wings. An adult wing with scales is differentiated from the pupal wing epithelium. The whole wing epithelium is not differentiated into the adult wing, but only the inner part of it is differentiated into it. The outer part is removed through programmed cell death at the early phase of the pupal period, which is closely related to the formation of a specialized wing margin with a fringe. In the inner part of the epithelium, scales are differentiated through two asymmetric cell divisions involving programmed cell death. The scales are homologous to the sensory bristles, but unlike the bristles, they are fairly flat, their upper and lower surfaces are morphologically different, and they are accompanied by no living cells. To provide basic information on the wing functions addressed in the subsequent eight chapters, the morphology and development of the wing are described in this chapter.