Evidence from folding and functional lines of wings on inter-ordinal relationships in Pterygota

Abstract

Insects fold their hind wings because of quite simple reasons. With fl exed and folded wings, it is easier to hide, to use small crevices and shelters against the impact of weather, e.g. wind and rain, and to escape predators, to name just a few reasons. The fi tness advantage is so great that wing folding convergently evolved in many separate insect ʻordersʼ (Heteroptera, Hymenoptera, Lepidoptera amongst others), using superfi cially different mechanisms. The Dermaptera, Blattodea and Coleoptera were examined in more detail. Included in the comparative study were other, technical and ornamental folded structures such as Origami models. The comparison showed despite very many differences some common features: almost all fold structures consist of Basic Mechanisms, an arrangement of four plates and four folding lines intersecting in one point. In hind wings, resilin is ample; energy is needed to unfold and/or fold the wings and prevents wear at critical locations in the wing. Often the folding lines in the wing are not morphologically differentiated (at least at LM and SEM level), but some specialised structures, typical for taxonomic families and orders do occur. The actual mechanics used in folding and unfolding, respectively, are fundamentally different: Coleoptera use their thoracic muscle to unfold the wing, but the elytra and the abdomen to fold it again. In Dermaptera, the wing is unfolded with the cerci, and folded with intrinsic elasticity stored in the many, strategically placed resilin patches. In Blattodea the wing unfolding is a simple by-product of wing promotion. Technical folded structure such as airplanesʼ wings are comparatively simple, and take advantage of the option to have additional tools & mechanisms for (un-)folding, as well interrupting the structural integrity for a short period of time. So they become unfunctional for a spell, which is no option for biological structures.