Insect Diversity

3.1. Origin and Evolution of Wings

The origin of insect wings has been one of the most debated subjects in entomology for close to two centuries, and even today the question remains far from being answered. Most authors agree, in view of the basic similarity of structure of the wings of insects, both fossil and extant, that wings are of monophyletic origin; that is, wings arose in a single group of ancestral apterygotes. Where disagreement occurs is with respect to (1) whether the wing precursors (pro-wings) were fused to the body or were articulated; (2) the position(s) on the body at which pro-wings developed (and, related to this, how many pairs of pro-wings originally existed); (3) the original functions of pro-wings; (4) the selection pressures that led to the formation of wings from pro-wings; and (5) the nature of the ancestral insects; that is, were they terrestrial or aquatic, were they larval or adult, and what was their size (Wootton, 1986, 2001; Brodsky, 1994; Kingsolver and Koehl, 1994).

At the core of all theories on the origin of wings is the matter of whether the pro-wings initially were outgrowths of the body wall (i.e., non-articulated structures) or were hinged flaps. Although there have been several proposals for wing origin based on non-articulated pro-wings (see Kukalova-Peck, 1978), undoubtedly the most popular of these is the Paranotal Theory, suggested by Woodward (1876, cited in Hamilton, 1971), and supported by Sharov (1966), Hamilton (1971), Wootton (1976), Rasnitsyn (1981), and others. The theory is based on three pieces of evidence: (1) the occurrence of rigid tergal outgrowths (wing pads) on modern larval exopterygotes (ontogeny recapitulating phylogeny); (2) the occurrence in fossil insects, both winged (Figure 2.5) and wingless (Figure 2.1B), of large paranotal lobes with a venation similar to that of modern wings; and (3) the assumed homology of wing pads and lateral abdominal expansions, both of which have rigid connections with the terga and, internally, are in direct communication with the hemolymph.

Essentially the theory states that wings arose from rigid, lateral outgrowths (paranota) of the thoracic terga that became enlarged and, eventually, articulated with the thorax. It presumes that, whereas three pairs of paranotal lobes were ideal for attitudinal control (see below), only two pairs of flapping wings were necessary to provide a mechanically efficient system for flight. (Indeed, as insects have evolved there has been a trend toward the reduction of the number of functional wings to one pair [see Chapter 3, Section 4.3.2]). This freed the prothorax for other functions such as protection of the membranous neck and serving as a base for attachment of the muscles that control head movement.

Various suggestions have been made to account for development of the paranota. For example, Alexander and Brown (1963) proposed that the lobes functioned originally as organs of epigamic display or as covers for pheromone-producing glands. Whalley (1979) and Douglas (1981) suggested a role in thermoregulation for the paranota, an idea that has received support from the experiments of Kingsolver and Koehl (1985) using models. Most authors, however, have traditionally believed that the paranota arose to protect the insect, especially, perhaps, its legs or spiracles. Enlargement and articulation of the paranotal lobes were associated with movement of the insect through the air. Packard (1898, cited in Wigglesworth, 1973) suggested that wings arose in surface-dwelling, jumping insects and served as gliding planes that would increase the length of the jump. However, the almost synchronous evolution of insect wings and tall plants supports the idea that wings evolved in insects living on plant foliage. Wigglesworth (1963a,b) proposed that wings arose in small aerial insects where light cuticular expansions would facilitate takeoff and dispersal.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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