1 General Introduction

1 General Introduction If the karate-ka (student) shall walk the true path, first he will cast aside all preference. Tatsuo Shimabuku, Grand Master of Isshin-ryu Karate 1.1 The Importance of Insects ~30% of the plants we grow for food and materials. Because of their great numbers and diversity, insects Insects transmit some of these pathogens. While have a considerable impact on human life and indus- weeds can often reduce pest attack, they can also try, particularly away from cities and in the tropics. harbour the pest’s enemies or provide alternative On the positive side they form a large and irreplace- resources for the pest itself. Then in storage, insects, able part of the ecosystem, especially as pollinators mites, rodents and fungi cause a further 30% loss. of fruit and vegetable crops and, of course, many Apart from such biotic damage, severe physical con- wild plants (Section 8.2.1). They also have a place ditions such as drought, storms and flooding cause in soil formation (Section 8.2.4) and are being used additional losses. For example, under ideal field increasingly in ‘greener’ methods of pest control. conditions new wheat varieties (e.g. Agnote and Biological control using insects as predators and Humber) would give yields of ~16 tonnes/ha, but parasites of pest insects has been developed in the produce typically about half this under good hus- West for over a century, and much longer in China. bandry. Pre-harvest destruction due only to insects More recently integrated pest management (IPM) is 10–13% (Pimentel et al., 1984; Thacker, 2002). and conservation biological control (CBC) are being Losses are probably higher in the Developing deployed to better effect. World. Hill (1997) and Boyer et al. (2012) estimate Entomology has played a major role in the devel- 30–40% of total crop losses globally. Polis (1999) opment of ecology and other branches of biology states ‘Worldwide, ... insects take about as much crop such as genetics, physiology and behaviour. This is production as is used by humans’, although other not only because insects form the major part of the data (Reynolds, 2012a) suggest that this estimate is terrestrial fauna, but also because they offer a con- too high. But without crop protection, chemicals venient method of study. Their relatively small size included, losses could be 30% higher than they are leads to easy handling and their abundance facilitates with it (Oerke, 2006). Over the years there has been sampling and, in turn, a numerical analysis of the a shift of expenditure – insects now cost us large results. Their main disadvantage is that there are too amounts for crop protection, hopefully to lessen many of them. So many orders, families and species their effect. The annual bill for agricultural insecti- exist that learning about their immense diversity cides is now approximately US$7 billion in North takes a long time and not inconsiderable effort. America, and more than US$20 billion worldwide. Also, many people are entomophobic: they just do Even so, their effectiveness is variable. Naturally, not like insects and proceed in ignorance to belittle these estimates are but a fraction of the total because their far-reaching effects on people and the envir- the costs of application and wasted time should onment. After you read this book you will not be also be put on the account. among them. This situation has promoted a huge research But of course, some insects have a negative side, effort, but since agriculture in its widest sense is the and in a few this side is considerable. Before harvest world’s biggest productive industry, and since research they, together with weeds and pathogens, destroy scientists are, in the main, dedicated people working © CAB International, 2020. Ecological and Economic Entomology: A Global Synthesis (ed. B. Freeman) 1 for low salaries, generally this has been cost effective. agriculture. There are direct and indirect effects. A Premiership footballer gets twice as much in a Both farmers and livestock may suffer insect bites, week as the average scientist gets in a year. Hopefully, become victims to their juvenile stages or get future generations will wonder at this past stupid- infected with insect-borne diseases such as malaria ity. One of the reasons why improving pest control and dengue. As we will see, only a few insect species is critical, is that although new crop varieties have are pests; most are beneficial. The number of import- greatly increased production (Oerke, 2006), trad- ant pests is around 0.1% of the vast number of itional crops had more innate resistance to insect described insect species (about 1000–2000 species damage. Traditional rice in Asia had losses of only a in total). With time, some species gain and others few per cent, while modern varieties can have losses recede in their importance. This is because new crops around 25%. Even so, they produce five times as are developed and grown and new forms of hus- much grain per hectare and that is the bottom line; bandry are devised, but also because agro-chemicals a basic principle. are misused. Insects also migrate and/or change The widespread use of insecticides, fungicides and under climatic and evolutionary influences, while weed killers has brought environmental pollution management is rarely fully informed. in its train. Conversely, in traditional African agriculture little is spent on chemicals, but losses from 1.2 Insect Size pests are very apparent. Environmental degrad- ation in Africa is due largely to deforestation; in In the scale of life, insects are of small to medium Europe that has happened already. Only if we can size. Mymarid wasps that parasitize insect eggs learn to manipulate our environment and agro- weigh <1 mg, while at the other end of the scale ecosystems in particular in permanent ways, with Goliath beetles may attain 40 g, a range >40,000 mg. low recurrent expenditure, would we have defeated Hamilton (1996, p. 386) provides an even greater enemy insects. This has been achieved in a few range: Titanus giganteus from palm logs in Brazil cases. But ‘permanent’ is euphemistic when applied to are a million times bigger than ptilinid beetles biological systems: the playing field is uneven and (Ptinella). Their size relative to other terrestrial the rules partly known. While limits exist (Arnold, animals, their size within the range for insects and 1992), evolution works constantly (Haldane, 1954; even their own species have basic consequences for Trivers, 1985), adjusting the positions of all the their physiology and ecology (Price, P.W., 1997). living players. We hear fables of fleas scaled to the weight of a Progress in our favour has continued for several man jumping over famous public buildings. This decades, but an idyllic final solution is still far off. nonsense is the result of a naïve linear scaling of Old organic insecticides such as DDT were applied at both weight and power. But weight is a cubic func- an average rate of 1 kg/ha; now alpha-cypermethrin tion of body length, whereas muscular power is is applied at around 10 g/ha. These developments only a squared function. Doubling in weight pro- come not only within the ambits of organic chem- duces much less than doubling in power. Small size istry, ecology, largely applied ecological entomology also allows insects to exploit the great physical and population dynamics (Berryman, 1991b), but variation in their environments (Section 10.1.1). also those of economics and management. And any Another critical effect is that the smaller the organ- system used to combat insects must dovetail into the ism, the greater its surface area (a squared func- control of other pests, agricultural practice in gen- tion) relative to its weight. Big animals are in the eral and into economics. The nearest to the ideal grip of gravity, little ones are more affected by sur- solution we have come are biological control and face effects. Small insects trapped in a film of water IPM, but these methods do not always work and there may be unable to free themselves. These relationships may still be an environmental backlash (Pimentel give us a glimpse into the foreign physical environ- et al., 1984). Related techniques of landscape man- ment of the insect, for example, how a fly can land agement and CBC are still being developed. But upside down on a ceiling. ignorance, lack of aesthetic awareness and avarice The world is relatively a much larger place for a continue to be important social factors. small animal than it is for a large one (Hutchinson, Insects attack not only our field, forest and orchard 1959; Morse et al., 1985). To continue with insect crops, but also our domesticated animals and our- size discussion, our mymarid wasp develops within selves, making it more difficult for us to practise the minute confines of a moth’s egg, but the larva 2 Chapter 1 of the big moth Manduca sexta may have to eat an and Denno, 1997; Marden, 2000). Insect size affects entire tomato plant for development. Many phyt- both mobility and reproduction. Insect flight muscle ophagous insects live inside their plant food (endo- is of two types: the synchronous or neurogenic type phytic). Some cereal beetles can live out their juvenile in which each neural stimulus produces a single lives within single grains. Indeed, the rather low contraction; and the asynchronous or myogenic metabolic rate of larval forms allows them to sur- type in which it produces multiple contractions. vive in cryptic places. Here oxygen is deficient, but Unsurprisingly, wing-beat frequency, wing loading, they avoid desiccation and predation.

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