1 1 Introduction – A Brief History of Revolutions in the Study of Insect Biodiversity Peter H. Adler1 and Robert G. Foottit2 1 Department of Plant and Environmental Sciences, Clemson University, Clemson, South Carolina, USA 2 Canadian National Collection of Insects, Arachnids, and Nematodes, Agriculture and Agri‐Food Canada, Ottawa, Ontario, Canada John Platt (1964), in his iconic paper “Strong Hennig’s procedural framework for inferring Inference,” asked “Why should there be such relationships. The revolutions of significance rapid advances in some fields and not in in understanding biodiversity (Fig. 1.1) have, others?” The answer, he suggested, was that therefore, largely been those that enabled and “Certain systematic methods of scientific enhanced (i) the discovery process, (ii) the con­ thinking may produce much more rapid pro­ ceptual framework, and (iii) the management of gress than others.” As a corollary to Platt’s information. (1964) query, we ask “Why, within a field, should there be such rapid advances at some times and not at others?” The answer, we sug­ 1.1 ­Discovery gest, is “revolutions” – revolutions in thinking and technology. Perhaps the most revolutionary of all the devel­ In the study of life’s diversity, what were the opments that enabled the discovery of insect revolutions that brought us to a 21st‐century biodiversity was the light microscope, invented understanding of its largest component – the in the 16th century. The first microscopically insects? Some revolutions were taxon specific, viewed images of insects, a bee and a weevil, such as the linkage of diseases to vectors were published in 1630 (Stelluti 1630). Other (e.g., mosquitoes), which necessitated the need excellent early examples of microscope‐enabled to discover and understand species. Others illustrations of insects, such as ants, fleas, flies, included all insect taxa, such as the develop­ and even a fold‐out centerfold of a louse, were ment of light microscopy.COPYRIGHTED Some were small, featured MATERIAL in Robert Hooke’s 1665 publication, such as the invention of the Malaise trap. Some Micrographia (Neri 2011). Improvements in were mighty, such as the molecular revolution. magnification and resolution over the next two As discovery revealed an ever‐increasing wealth centuries ensured that the microscope would of biodiversity, patterns began to emerge. The continue as the primary enabler of insect biodi­ organization and explanation of these pat­ versity research. By the time light microscopy terns received quantum boosts from Carolus had achieved its theoretical limit of resolution Linnaeus’s systems of classification and nomen­ in the late 1800s, the study of insects and their clature, Charles Darwin’s natural explanation diversity had become a well‐established enter­ for species and their relationships, and Willi prise, although still largely descriptive in nature. Insect Biodiversity: Science and Society, Volume II, First Edition. Edited by Robert G. Foottit and Peter H. Adler. © 2018 John Wiley & Sons Ltd. Published 2018 by John Wiley & Sons Ltd. c01.indd 1 3/22/2018 3:58:02 PM 2 Insect Biodiversity: Science and Society 1590 Light microscope is invented 1840s: “At the end of the abdomen are placed 1600 the anal appendages, an examination of which is First microscopically viewed imperative for the correct discrimination of 1630 insects are illustrated species. Already, in 1842, Rambur had become 1635 France's Muséum National d'Historie Naturelle fully alive to the importance of these charac­ becomes first modern museum ters…” (McLachlan 1874, p. 6). As genitalia were 1660 analyzed for each group, the number of species increased. For example, the number of spe­ First dichotomous identification key is produced 1689 cies of black flies (Simuliidae) described from 1700 Linnaeus’s “backyard” (Fennoscandia) doubled 1720 in 1911, the year genitalia were introduced as Réné Réaumur publishes natural history taxonomic characters for the family (Lundström 1734 monographs on insect species 1911). And following the introduction of geni­ Linnaeus's Systema Naturae 10th edition talic characters for leafhoppers (Cicadellidae) in 1758 establishes beginning of modern zoological nomenclature 1922 (DeLong 1922), the discovery of new spe­ 1780 cies surged. Thomas Say publishes first With the microscope came the development comprehensive taxonomic treatment 1800 of insects in the New World of new preparation and preservation techniques (Bracegirdle 1998). Glass microscope slides, ini­ Insect genitalia are introduced as 1824 taxonomic characters tially with coverslips of mica, became dominant 1840 Chromosomes are discovered in the 1800s, and by the 20th century, coverslips Charles Darwin's On the Origin of Species of glass with standardized thickness became the 1859 is published arrangement routinely used today. The early US Taxonomic value of non-morphological federal entomologist Theodore Pergande was 1880 characters (e.g., sound production) recognized Glass microscope slides with Canada balsam using microscope slides with Canada balsam to and glass coverslips are used for insects preserve and study aphids as early as the 1870s Figure 1.1 Selected highlights in the insect biodiversity (Miller and Foottit 2017). The early choice of time line. Canada balsam, a natural product from the bal­ sam fir (Abies balsamea), as a mounting medium has ensured that slides prepared more than 100 years ago are still interpretable today. Additional developments in microscopy, includ­ When human interests collide with insects, ing those used routinely by researchers, such as science progresses. Threats to food, fiber, phase‐contrast microscopy (invented in the health, and shelter have led to dramatic leaps in early 1930s) and scanning electron microscopy discovering and understanding insect biodiver­ (first commercially available in the 1960s), sity. In the early 1800s, Rafinesque described 36 improved the ability to interpret, although species of aphids, prompted by his recognition rarely to discover, structural characters. The that these tiny insects are often deleterious light microscope, however, remains the most to their host plants (Miller and Foottit 2017). fundamental tool in insect biodiversity research. Thaddeus Harris’s splendid 1841 book and sub­ The microscope enabled an explosion of dis­ sequent expanded editions provided the vade coveries of new species and new characters that mecum for dealing with the scourges of agri­ permitted refinements in classification and culturally important insects and a foundation identification. The study of insect genitalia, for for future biodiversity exploration. In Harris’s instance, would not have been possible before (1841) words, “Some knowledge of the classifi­ the microscope. The scientific value of insect cation of insects … seems to be necessary to the genitalia was well understood by the early farmer, to allow him to distinguish his friends c01.indd 2 3/22/2018 3:58:02 PM 1 Introduction 3 from his enemies of the insect race.” The Édouard-Gérard Balbiani discovers 1881 polytene chromosomes ­agricultural ravages of Lygus, for example, even­ 1883 Charles V. Riley suggests the existence of tually demanded deeper understanding of the what became known as cryptic species pests and helped to launch the career of noted 1893 Concept of type specimens is formalized mirid specialist Harry Knight (1917), who went 1897 Ronald Ross links malaria to mosquitoes on to describe 1345 species of plant bugs 1900 Berlese funnel is invented (Schuh 1995). 1905 Thomas H. Morgan initiates insect The year 1897 brought about a revolutionary genetic studies with Drosophila 1911 improvement to human health and ensured that Charles P. Alexander describes the first mosquitoes would become one of the taxonom­ of more than 10,000 crane fly species ically best‐known groups of insects on the 1920 planet. That was the year Ronald Ross (1897) Frits Zernike invents phase-contrast found malarial parasites in the gut of a “dappled‐ 1930 microscopy winged mosquito” (Anopheles sp.). As the focus 1934 Malaise trap is invented on vectors intensified, taxonomists bore down Ernst Mayr introduces the on the question of species and their differential 1942 biological species concept vectorial competency. Complexes of cryptic First edition of the International Code of Zoological Nomenclature is published species eventually were revealed (Coluzzi et al. 1950 2002). The genera with the most notorious vec­ Scanning electron microscopes become commercially available tors, Aedes and Anopheles, became some of the English-language version of Willi Hennig’s taxonomically best‐known mosquitoes. At least 1961 Phylogenetic Systematics is published Electronic databases, keys and computer- 75 species of Anopheles are now known to trans­ 1966 based analyses introduced mit malarial agents to humans (Foster and 1970 Electrophoresis-based taxonomy of insects Walker 2009). At a finer scale, the Anopheles becomes widely used gambiae complex includes the most efficient 1977 Fred Sanger introduces the chain-termination method for DNA sequencing 1982 malarial vectors. From genes to organisms, this Terry Erwin’s fogging of tropical canopy 1983 species complex ranks among the most taxo­ suggests 30 million insect species nomically well‐studied groups of insects. The Polymerase chain reaction (PCR) developed inevitable conclusion is that the degree of taxo­ by biochemist Kary Mullis nomic activity and sophistication is correlated Genome sequenced for Drosophila melanogaster with