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Insect Diversity

1. Introduction

In this chapter, we shall examine the evolutionary development of the tremendous variety of insects that we see today. From the limited fossil record it would appear that the earliest insects were wingless, thysanuranlike forms that abounded in the Silurian and Devonian periods. The maaor advance made by their descendants was the evolution of wings, facilitating dispersal and, therefore, colonization of new habitats. During the Carboniferous and Permian periods there was a massive adaptive radiation of winged forms, and it was at this time that most of the modern orders had their beginnings. Although members of many of these orders retained a life history similar to that of their wingless ancestors, in which the change from juvenile to adult form was gradual (the hemimetabolous or exopterygote orders), in other orders a life history evolved in which the juvenile and adult phases are separated by a pupal stage (the holometabolous or endopterygote orders). The great advantage ofhaving a pupal stage (although this is neither its original nor its only significance) is that the juvenile and adult stages can become very different from each other in their habits, thereby avoiding competition for the same resources. The evolution of wings and development of a pupal stage have had such a profound effect on the success of insects that they will be discussed as separate topics in some detail below.

2. Primitive Wingless Insects

The earliest wingless insects to appear in the fossil record are Microcoryphia (Archeognatha) (bristletails) from the Lower Devonian of Quebec (Labandeira et al., 1988) and Middle Devonian of New York (Shear et al., 1984). These, together with fossil Monura (Figure 2.1A) and Zygentoma (silverfish) (Figure 2.1B) from the Upper Carboniferous and Permian periods, constitute a few remnants of an originally extensive apterygote fauna that existed in the Silurian and Devonian periods. Primitive features of the microcoryphians include the monocondylous mandibles which exhibit segmental sutures, fully segmented (i.e., leglike) maxillary palps with two terminal claws, a distinct ringlike subcoxal segment on the meso- and metathorax (in all remaining Insecta this becomes flattened and forms part of the pleural wall), undivided cercal bases, and an ovipositor that has no gonangulum.

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FIGURE 2.1. Reconstructions of (A) Dasyleptus sp. (Monura); and (B) Rams-delepidion schusteri (Zygentoma). [From J. Kukalova-Peck, 1987, New Carboniferous Diplura, Monura, and Thysanura, the hexapod ground plan, and the role of thoracic side lobes in the origin of wings (Insecta), Can. J. Zool. 65:23272345. By permission of the National Research Council of Canada and the author.]

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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