HostParasiteDiscreteModels

HostParasiteDiscreteModels - Host-Parasite Models and...

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Unformatted text preview: Host-Parasite Models and Biological Control September 9, 2010 Introduction Classical biological control is the purposeful introduction and establishment of one or more natural enemies from the region of origin of an exotic pest, specifically for the purpose of suppressing the abundance of the pest in a new target region to a level at which it no longer causes economic damage (DeBach, 1964; DeBach and Rosen, 1991). Pests that can be controlled through natural enemy introductions include invertebrates, vertebrates, weeds and plant diseases, but here we confine our attention to insect pests as the most frequently used targets of classical biological control. The organisms that function as natural enemies of insect pests include vertebrate predators (e.g., birds, reptiles, amphibians and fish), invertebrate predators (primarily arthropods), parasitoids (holometabolous insects that live parasitically during their larval stage on a single individual of an arthropod host, causing the death of the host), other macroparasites (primarily nematodes), and microparasites or microbial pathogens (viruses, bacteria, fungi and protozoa). We again restrict our attention to just one group of natural enemies, the parasitoids, which are the most frequently used group of natural enemies in classical biological control and historically have been the focus for models of biological control. Classical biological control of insect pests, henceforth referred to as biological control, began in 1888 when the now legendary predator, the vedalia beetle (which functions as a parasitoid), was imported from Australia and established in California, where it very rapidly suppressed populations of the cottony cushion scale that had been decimating the developing citrus industry (Caltagirone and Doutt, 1989). This pioneering project was spectacular for several reasons; (a) it reduced populations of the pest to very low densities, where they remain to this day unless disrupted by the intervention of broad-spectrum insecticides, (b) it provided the first experimental evidence that parasitoids can act as keystone species determining the functioning and organization of an agroecosystem, and (c) it generated tremendous interest and activity in promoting the use of parasitoids for the control of invading pests throughout the world. 1 To date there have been more than 3600 purposeful introductions of parasitoids against more than 500 arthropod pests in almost 200 countries and islands around the world (Greathead and Greathead, 1992). In contrast, very few introductions of microbial pathogens have been attempted, for reasons documented by Maddox et al. (1992). Not all introductions have been as successful as the vedalia example, in fact only 30% of introductions have resulted in establishment of the natural enemy in the target region, and of these, only 36% have resulted in substantial or complete control of the target pest (Greathead and Greathead, 1992). The elusive nature of success in biological control was apparent to even the earliest researchers involved in such...
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HostParasiteDiscreteModels - Host-Parasite Models and...

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