Part 2 Historical, Theoretical, and Philosophical Bases of Biological Insect Pest Suppression

Part 2 Historical, Theoretical, and Philosophical Bases of Biological Insect Pest Suppression The practice of various biological methods of insect pest suppression has gained increasing acceptance, indeed popularity, in very recent years. A number of stim uli have led to this situation, not the least of which is the overall popular environ mental awareness which followed the publication of Rachel Carson's Silent Spring in 1962. But, as we shall see, an elegant and complex concept like biologi cal insect pest suppression does not gain stature and prominence overnight, nor does it spring full-flower from the mind of any single person. Historically, the growth of the discipline was slow and sometimes painful; it is studded with a few sparkling success stories, some disappointments, and many unheralded applica tions that are highly successful, but doomed to obscurity because of that very success. Indeed, the results of a successful program of biological pest suppression are not very impressive unless the situation can be compared to that which existed previously. In the following three chapters we shall touch on some of the high lights in the development of the ideas and practices of "classical" biological insect pest suppression-this is, the directed use of parasitoids, predators, and patho genic microorganisms to reduce and regulate insect pest populations to subecon omic levels. Some of the more recently developed aspects and agencies of biologi cal insect pest suppression are dealt with in greater detail later (Part 4). The earliest observational, intuitive, and empirical work discussed in Chapter 2.1 led to the recognition and appreciation of some basic ecological principles and the theories of population dynamics discussed in Chapter 2.2. In Chapter 2.3, these and other ecological concepts are presented in their philosophical relationship to the classical practice of biological insect pest suppression. 2.1 Historical Development 2.1.1 Early History to 1888 To discover the origins of the practice that is today known as biological control one must look deeply into the dim reaches of human prehistory. Surely long before the rise of humankind and the first slow faltering steps in the development of agriculture, insects were subject to interaction with other inhabitants of the biosphere. Some of these interactions were beneficial to the individual insect (e.g. supplied nutriment, protection, or other advantageous symbiotic relations), and some were detrimental (e.g. competition, disease, predation). All such interactions were necessary, for if the species was to survive in nature it had to do so in concert with other organisms, producing neither too many nor too few individuals for a H. C. Coppel et al., Biological Insect Pest Suppression © Springer-Verlag Berlin · Heidelberg 1977 Early History to 1888 15 sustained stable population in a given environment. A biologist known as Charles Darwin was later to recognize this process and discuss it in great detail. Entomophagy, then, existed from the appearance of the first insects. These small comparatively vulnerable animals fell prey to all manner of predators, parasites, and diseases, some of which came to depend on them entirely for food. No one knows with certainty when "the knowing man," Homo sapiens, first became cognizant of entomophagy by other animals, but early humans them selves probably utilized insects as part of their own diet much as many primitive peoples do today. It seems reasonable to assume that the simple fact of predation was recognized at an early date, because man was himself sometimes competing with other insect predators for the same food source, but the more subtle ideas of parasitism probably remained beyond comprehension for hundreds of years. Some insect diseases produce such spectacular effects that even primitive man must have noticed them and perhaps compared them to the afflictions of larger animals, though we have no evidence of this observation (Steinhaus, 1956). The discovery of agriculture and its development during Neolithic times, about 10000 B.C., put humankind into very direct competition with insects for food. With the coming of crop raising and monoculture came a localized abund ance of certain plant foods, and inevitably a localized increase in the abundance of pests to utilize them. We know that as agriculture progressed in sophistication a certain amount of selection took place in the varieties of crop plants grown. Most notably selected were strains giving greater yields through larger or more numer ous seeds, fruits, or tubers, but other desirable qualities were probably also noted and encouraged. Thus the selection of crop varieties exhibiting resistance to disease and insect pests can be considered the oldest practical application of a type of biological pest suppression. Just as early man observed birds eating insects, and snakes eating rodents in the woods and fields, he must also have noted the proclivity of certain wild felines toward a diet of mice and rats like those which infested his stores of grain and other foods. And so, the domestication of the house cat by the ancient Egyptians may well have been encouraged in part by this useful habit, and may be consi dered as a second very early attempt at biological pest suppression. We may now move from the realm of conjecture to the world of recorded facts. In the Bible we encounter the various plagues which befell Egypt, and in the first chapter of the Book of Joel a series of insect depredations is described which later disappear, illustrating the early recognition of the cyclical nature of pest populations. As with many other aspects of biology, the writings of the ancient Greek and Roman naturalists contain some of the earliest recorded information pertinent to the subject at hand (Smith and Secoy, 1975). A number of the classical philosophers had things to say about insects, but few are as valuable or accessible as the writings of Aristotle and Pliny (Marlatt, 1898). Within the masses of general observations and descriptions covering various aspects of insect study can be found early references to insect pathology. Aristotle (384-322 B.c.), in his Histo ria Animalium, described the ravages of the wax moth to honeycomb, and suggests that it brings "disease into the swarm" (Steinhaus, 1956). He further describes other disease symptoms in bees which may be interpreted as a foulbrood condi tion. Similarly the Roman author, Pliny (23-79 A.D.), recognized several disease 16 Historical, Theoretical, and Philosophical Bases of Biological Insect Pest Suppression conditions in bees. In another part of the world another domestic insect, the silkworm, also suffered from various afflictions, some of which were recognized as early as 1000 A.D. (Steinhaus, 1956). In all of these instances, however, not much of real practical value was presented or suggested; the ancient naturalists and philosophers contented themselves with simple observation and description, and it was not until after the Dark and Middle Ages that anything substantially new was added to the body of practical knowledge concerning natural mortality in insects. We are aware of two notable exceptions to this statement. Although insect predation was observed and recognized for a long time, the idea of actually using predatory animals for agricultural pest control was slow to germinate. What is apparently the first known use of this method, which is true biological insect suppression in the modern sense, was the practice by Chinese citrus growers of introducing predaceous ants into their groves (Liu, 1939). An old Chinese book called "Wonders from Southern China," published about 900 A.D., speaks of the availability in the local markets of large yellow ants with long legs (probably Oecophylla smaragdina F.) used to protect oranges from "wormy" fruit. Another writer mentioned the same fact in the 1300s and as late as 1939 ant nests were still for sale in the markets of Canton. McCook (1883) commented on a Chinese newspaper report of the method, and discussed the possibilities of using these ants or native species for pest suppression in the United States. A second, and similar instance of early biological control was the practice of the date growers of the Mideastern country of Yemen, who moved colonies of beneficial ants to their groves from the mountains each year for insect pest suppression (Botta, 1841). It was not long after the reestablishment of intellectual activity in Europe that new and valuable observations on the natural history of insects began to appear. In the sixteenth and early seventeenth centuries the renewed interest in science resulted mostly in the repetition ofthe beliefs of the ancients supplemented in part by original observation. Names like Gesner, Thomas Mouffet, and Aldrovandi characterize the times. Mouffet's 1heatrum Insectorum (which included Gesner's work) was published posthumously in 1634, and was the first book written exclu sively about insects. The book discussed or figured such things as diseases and parasites of bees and a nematode-infected silkworm (Ordish, 1967). Although Mouffet's book was the first book written on insects, Ulysses Aldrovandi's De Animalibus Insectis was the first volume published on the subject in 1602. It summarized all the material previously written on insects and included the first published record of insect parasitism. An attack of the gregarious braconid paras itoid, Apanteles glomeratus (L.), on the cabbage butterfly, Pieris rapae (L.), was shown, but misinterpreted by Aldrovandi, who thought the conspicuous parasi toid cocoons were insect eggs. In 1668, the Italian, Francesco Redi, described the same phenomenon and also parasitism of aphids by an ichneumon "fly." Redi also deserves credit for disproving the doctrine of spontaneous generation of life from nonliving material, but it was not until 1706 that Vallisnieri correctly inter preted all of these early observations on insect parasitism. The literature of the eighteenth century produced numerous other references to insect predators and parasitoids as naturalists began to question the works of antiquity and investigate the living world for themselves.

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