Development And Life Histories

Life-cycle phases of the monarch or wanderer butterfly, Danausplexippus. (After photographs by P.J. Gullan.)

In this chapter we discuss the pattern of growth from egg to adult - the ontogeny - and life histories of insects. The various growth phases from the egg, through immature development, to the emergence of the adult are considered. Molecular insights into the embryo-logical development of insects are discussed in a box. We discuss the significance of different kinds of metamorphosis and suggest that complete metamorphosis reduces competition between conspecific juveniles and adults, by providing a clear differentiation between immature and adult stages. Amongst the different aspects of life histories covered are voltinism, resting stages, the coexistence of different forms within a single species, migration, age determination, allometry, and genetic and environmental effects on development. We include a box on a method of calculating physiological age, or day-degrees (degree-days). The influence of environmental factors, namely temperature, photoperiod, humidity, toxins, and biotic interactions, upon life-history traits is vital to any applied entomological research. Likewise, knowledge of the process and hormonal regulation of molting is fundamental to insect control.

Insect life-history characteristics are very diverse, and the variability and range of strategies seen in many higher taxa imply that these traits are highly adaptive. For example, diverse environmental factors trigger termination of egg dormancy in different species of Aedes although the species in this genus are closely related. However, phylogenetic constraint, such as the restrained instar number of Nepoidea (Box 5.5), undoubtedly plays a role in life-history evolution in insects.

We conclude the chapter by considering how the potential distributions of insects can be modeled (including a box on climatic modeling for fruit flies), using data on insect growth and development to answer questions in pest entomology, and bioclimatic data associated with current-day distributions to predict past and future patterns.

Thus this chapter describes the patterns of insect growth and development and explores the various environmental, including hormonal, influences on growth, development, and life cycles. We do not attempt to explain why different insects look the way that they do, i.e. how their morphology evolved to produce the observable differences in body form among species and higher taxa. However, recent advances in evolutionary developmental biology (evo-devo) have provided a mechanistic framework as a hypothesis to help explain the evolution of morphological diversity. Research on Drosophila species, for which both the genome and the pattern of development are relatively well understood, has shown that: "(1) form evolves largely by altering the expression of functionally conserved proteins, and (2) such changes largely occur through mutations in the cis-regulatory sequences of pleiotropic developmental regulatory loci and of target genes within the vast networks they control." (Carroll, 2008: 3). For example, the Hox proteins of arthropods have highly conserved sequences across the various arthropod groups, but their expression varies substantially among major taxa (Box 6.1). At the level of species, differences in morphology (such as the differing patterns of pigmentation on the wings and abdomen of adult flies of closely related Drosophila species) can be explained by changes in the cis-regulatory elements that control the expression of the genes that code for pigmentation. More detailed information on the genetics of morphological evolution are beyond the scope of an entomology textbook, and we refer interested readers to Box 6.1 and to articles listed in the Further Reading section at the end of this chapter.

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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