OCCURRENCE AND STRUCTURE OF WINGS

Fully developed and functional wings occur only in adult insects although the developing wings are present in larvae. In hemimetabolous larvae they are visible as external pads (section 15.3.1), but they develop internally in holometabolous species (section 15.3.2.2). The Ephemeroptera are exceptional in having two fullywinged stages. The final larval stage molts to a subimago, which resembles the adult except for having fringed and slightly translucent wings and rather shorter legs. It is able to make a short flight, after which it molts and the adult stage emerges. In the course of this molt the cuticle of the wings is shed with the rest of the cuticle.

The fully developed wings of all insects appear as thin, rigid flaps arising dorsolaterally from between the pleura and nota of the meso- and meta-thoracic segments. Each wing consists of a thin membrane supported by a system of veins. The membrane is formed by two layers of integument closely apposed, while the veins are formed where the two layers remain separate and the cuticle may be thicker and more heavily sclerotized (Fig. 9.1). Within each of the major veins is a nerve and a trachea, and, since the cavities of the veins are connected with the hemocoel, hemolymph can flow into the wings (section 5.1.2.1).

Basic structure of the wing

The structure of the wing is determined primarily by the need to optimize the production of favorable aerodynamic forces during flight.