The Insects

An Outline of Entomology

P. J. Gullan, P. S. Cranston

• Editore: Wiley-Blackwell
• Anno: 2014
• ISBN:
  9781118846162
• Edizione: 5
• Argomento: Biological Sciences
• Categoria: Entomology

Insects represent over half of the planet's biological diversity. This popular textbook provides a comprehensive introduction to this extraordinary diversity, and places entomology central to the theory and practice of evolutionary and ecological studies.

Fully revised, this fifth edition opens with a chapter concerning the popular side of insect studies, including insects in citizen science, zoos and butterfly houses, and insects as food for humans and animals. Key features of insect
structure, function, behaviour, ecology and classification are integrated with appropriate molecular studies. Much of the book is organized around major biological themes: living on the ground, in water, on plants, in colonies, and as predators, parasites/parasitoids and prey insects. A strong evolutionary theme is maintained throughout.

There is major revision to the chapter on systematics and a new chapter, Insects in a Changing World, includes insect responses to, and the consequences of, both climate change and human-assisted global alterations to distributions. Updated 'Taxoboxes' demonstrate topical issues and provide concise information on all aspects of each of the 28 major groupings (orders) of insects, plus the three orders of non-insect hexapods. New boxes describe a worrying increase in insect threats to landscape and commercial trees (including eucalypts, palms and coffee) and explain the value of genetic data, including evolutionary developmental biology and DNA barcoding, in insect biodiversity studies. The authors maintain the clarity and conciseness of earlier editions, and extend the profuse illustrations with new hand-drawn figures. Over 50 colour photographs, together with the informative text and an accompanying website with links to video clips, appendices, textboxes and further reading lists, encourage a deeper scientific study of insects. The book is intended as the principal text for students studying entomology, as well as a reference text for undergraduate and graduate courses in the fields of ecology, agriculture, fisheries and forestry, palaeontology, zoology, and medical and veterinary science.

Chapter 1
The Importance, Diversity and Conservation of Insects

Charles Darwin inspecting beetles collected during the voyage of the Beagle. (After various sources, especially Huxley & Kettlewell 1965 and Futuyma 1986.)

Curiosity alone as to the identities and lifestyles of the fellow inhabitants of our planet justifies the study of insects. Some of us have used insects as totems and symbols in spiritual life, and we portray them in art and music. If we consider economic factors, the effects of insects are enormous. Few human societies lack honey, which is provided by bees (or specialized ants). Insects pollinate our crops. Many insects share our houses, agriculture and food stores. Others live on us, on our domestic pets or our livestock, and more visit to feed on us, where they may transmit disease. Clearly, we should understand these pervasive animals.

Although there are millions of kinds of insects, we do not know exactly (or even approximately) how many. This ignorance as to how many organisms we share our planet with is remarkable considering that astronomers have listed, mapped and uniquely identified a comparable diversity of galactic objects. Some estimates, which we discuss in detail later, imply that the species richness of insects is so great that, to a near approximation, all organisms can be considered to be insects. Although dominant on land and in freshwater, few insects are found beyond the tidal limit of oceans.

In this opening chapter, we outline the significance of insects and discuss their diversity and classification, and their roles in our economic and wider lives. First, we outline the field of entomology and the role of entomologists, and then introduce the ecological functions of insects. Next, we explore insect diversity, and then discuss how we name and classify this immense diversity. Sections follow in which we consider some cultural and economic aspects of insects, their aesthetic and tourism appeal, their conservation, and how and why they may be reared. We conclude with a section on insects as food for humans and animals. In text boxes we discuss citizen involvement in entomology (Box 1.1), the phenomenal growth of butterfly houses (Box 1.2), the effects of tramp ants on biodiversity (Box. 1.3), the conservation of the large blue butterfly in England (Box 1.4) and insect threats to palm trees (Box 1.5).

1.1 WHAT IS ENTOMOLOGY?

Entomology is the study of insects. Entomologists are the people who study insects, and observe, collect, rear and experiment with insects. Research undertaken by entomologists covers the total range of biological disciplines, including evolution, ecology, behaviour, anatomy, physiology, biochemistry and genetics. The unifying feature is that the study organisms are insects. Biologists work with insects for many reasons: ease of culturing in a laboratory, rapid population turnover, and availability of many individuals are important factors. The minimal ethical concerns regarding responsible experimental use of insects, as compared with vertebrates, are a significant consideration.

Modern entomological study commenced in the early 18th century when a combination of rediscovery of the classical literature, the spread of rationalism, and the availability of ground-glass optics made the study of insects acceptable for the thoughtful privately wealthy. Although today many people working with insects hold professional positions, some aspects remain suitable for informed citizens (Box 1.1). Charles Darwin's initial enthusiasm in natural history was as a collector of beetles (as shown in the vignette for this chapter) and throughout his life he communicated with amateur entomologists throughout the world. Much of our present understanding of worldwide insect diversity is derived from studies of non-professionals. Many such contributions come from collectors of attractive insects such as butterflies and beetles, but others with patience and ingenuity continue the tradition of Jean-Henri Fabre in observing close-up the activities of insects. We can discover much of scientific interest at little expense regarding the natural history of even “well-known” insects. The variety of size, structure and colour in insects (see Plate 1a–f) is striking, whether depicted in drawings, photographs or movies.

A popular misperception is that professional entomologists emphasize killing or controlling insects, but numerous entomological studies document their beneficial roles.

1.2 The importance of insects

There are many reasons why we should study insects. Their ecologies are incredibly variable. Insects may dominate food chains and food webs in terms of both volume and numbers. Feeding specializations of different insect groups include ingestion of detritus, rotting materials, wood and fungus (Chapter 9), aquatic filter feeding and grazing (Chapter 10), herbivory

, including sap feeding (Chapter 11), and predation and parasitism (Chapter 13). Insects may live in water, on land, or in soil, during part or all of their lives. Their lifestyles may be solitary, gregarious, subsocial or highly social (Chapter 12). They may be conspicuous, mimics of other objects, or concealed (Chapter 14), and may be active by day or by night. Insect life cycles (Chapter 6) allow survival under a wide range of conditions, such as extremes of heat and cold, wet and dry, and unpredictable climates.

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Box 1.1 Citizen entomologists—community participation

The involvement of non-professional “citizen scientists” in biodiversity studies dates back at least to the 18th century, especially in the United Kingdom. Published guides to the fauna became best-sellers—Victorian ladies of leisure studied the flora and collected shells and fossils, wealthy gentlemen shot rare birds and collected their eggs, and the rich assembled “cabinets of curios” that became the world-renowned natural history collections of the great museums. Darwin, portrayed in the vignette at the beginning of this chapter, was a skilled collector and student of the Coleoptera, and many church curates, with little to do between Sunday sermons, were serious entomologists at a time when few were paid for such studies.

Despite the transformation of natural history into a professional science, areas such as floristics and ornithology continue to benefit from amateur involvement. The ever-increasing availability of internet-based guides to images, distribution maps, bird-songs, etc., encourages involvement of citizens in recording many facets of the biota of their local areas. The more popular insects are also subjects of interest to a wider public, and there is substantial participation in reporting occurrences, particularly for butterflies, dragonflies, wasps and bees, and beetles. Especially in Europe and North America, many can be identified (some more easily than others) without killing the insect, by eye or by using a hand lens. With digital photography, excellent macro-images can be passed to experts for confirmation of identification, used to “voucher” observations, and validated records then can be entered into databases. Citizen-collected records are valuable in establishing distributions and temporal presence (e.g. early and late dates for appearance)—and have assisted in documentation for conservation and for assessing effects of climate change.

The longest lasting, and surely largest, participatory survey, the Rothamsted Insect Survey, has used light-traps at over 430 sites in the United Kingdom, many operated by volunteers, since the 1960s. More than 730 species of macrolepidoptera have been recognized since the survey began, and more than 10 million data points

have been databased. Although this resource is used widely to infer effects of climate change, most studies infer that observed declines in lepidopteran populations relate more to the staggering loss of natural habitats to agriculture, with climate effects evident most in the previous years' summer conditions.

In the United States, citizen scientists have been recruited to collect long-term data on sightings of migrating butterflies, eggs and larval populations of the monarch butterfly (Danaus plexippus) and its milkweed habitat. Volunteers contribute to monarch conservation by regular monitoring of their local sites. One major goal is to understand how and why monarch populations vary in time and space, particularly during the breeding season in North America.

The United Kingdom's Ladybird Survey provides another example of public participation in insect recording. Ladybirds (called lady beetles or ladybugs in the United States; a pair of copulating adults is illustrated here) are common, colourful, and can be identified with appropriate guidance (using a “Ladybird Atlas”) built on several pre-existing specialist recording schemes. A website (http://www.ladybird-survey.org/) provides much information to help find and identify species, and provides online forms to record observations. There is great value in this scheme, as evidenced by the recent invasion of the United Kingdom by the East Asian harlequin ladybird (Harmonia axyridis); documentation of its spread and the impact on native ladybirds has been possible due to existing community surveys. Such a project requires a good existing database: the impacts of this introduced species in the United States can only be surmised as pre-invasion data are inadequate.

Global recording of odonates (dragonflies and damselflies) by amateurs is very popular, especially in Asia. As with small birds, identifications can be made at some distance using binoculars (as illustrated here). Photographic vouchers can be taken while the insects are sedentary (e.g. at dawn). Care must be taken though not to assume that the presence of adult odonates indicates water conditions suitable for nymphal development since adults are strong flyers (see section 10.5 on biomonitoring).

As with all observational data, appropriate checks on identifications are important and observer biases often occur. Thus citizen-science data should be interpreted with caution, a...