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C  Ecological Theory and Biological Control of Insect Pests   .  Department of Ecology, Evolution, and Marine Biology University of California–Santa Barbara The Department of Entomology at Texas A&M University has played an important role in the development of many areas of entomology that have bene fited society, including the area of pest control, which will be my main topic. The area of entomology I will discuss is population ecology, and especially population dynamics, which studies the abundance of organisms. Within that broad discipline, ecology-in-entomology has served human society most directly through helping to control pests in agriculture, especially via biological control of pests, which will be the focus of my talk. Before discussing biological control, I want to point out that entomology has made a much broader contribution to society. First, entomologists are probably the main group of scientists to have developed and expanded the theory of population dynamics, and such theory underlies successful resource management. For example, the successful management of fisheries relies on concepts such as density-dependence in whose development entomologists played a key role. Perhaps less obvious is that the modern theory of biological conservation has its origins in entomological studies. This is not broadly appreciated, since we usually think of conservation as applying to cute and charismatic organisms like cheetahs and the spotted owl. However, the central problem in conservation today is how to conserve species and biodiversity in an environment that is becoming progressively fragmented by agriculture, development, and the destruction of habitat. The theory behind conservation biology began with an entomological problem. The origin of the theory is modeled in  by Levins, who was interested in the problem of how best to control a pest population that existed in a patchy environment, such as a set of agricultural fields. He was interested in what happened if you managed to drive the pest extinct in some fields that were later re-colonized from other areas. These are models for what is now called metapopulation dynamics. Extensions of this theory are the basis of modern approaches to the design of habitat reserves for the entire range of conservation targets from the spotted owl in the United States to native forests and mammals in Australia. Furthermore, spatial studies of insects have been the major source of observational and experimental data that have tested metapopulation theory. Insects thus serve as the main model for conservation biology. A famous example is provided by a checkerspot butterfly (Euphydryas editha [Boisduval]) in Finland . In Finland this species is found only in dry meadows distributed across a small set of islands in the Baltic Sea. Studies over the past twenty years have shown that the butterfly is present at any one time in only about  percent of the , meadows. Each year, the butterfly goes extinct on  to  percent of these meadows. But the entire population persists because each year the butterfly also colonizes about the same number of new sites. The regional population thus persists in spite of local extinction. This study provides evidence that we might be able to preserve species on fragments of habitats, provided they are sufficiently interconnected. Let’s turn now to my main topic, the link between population ecology and biological control of insect pests. For those of you unfamiliar with biological control, it is broadly the use of natural enemies, such as predatory and parasitic insects, to control pests, mainly insects. In classical biological control , which I will focus on, the problem is that an insect that is not a pest in its area of origin, China for example, is accidentally introduced into a new area, such as the United States. It becomes a pest, and entomologists reason that it must be suppressed to low densities in its area of origin by its natural enemies—insect predators and parasites—and has escaped such control in the new area. They therefore go to China, find natural enemies, and import and release them to attack the pest. Success occurs when the pest is reduced to a low density, and remains there over long periods. Classical biological control has been successful for more than  years. More than  species ( percent of those targeted) have been brought under control. And of course a single success actually represents many successes. For example, the cottony-cushion scale (Icerya purchasi Maskell), a pest of citrus, has been controlled by the famous Vedalia beetle (Rhodolia cardinalis [Mulsant]) in many areas in each of fifty countries for up to...

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