Landmark Examples in Classical Biological Control

Abstract

Classical biological control, as it is commonly understood, is the regulation of a pest population (insect, mite, mammal, weed, pathogen) by exotic natural enemies (parasites, predators, pathogens) that are imported for this purpose. Usually, the target species (pest) is an exotic that has reached higher population density in the new environment because of more favor­ able conditions than in its area of indigeneity. The favorable conditions may include the lack of natural enemies capable of regulating the pest population to lower levels. In these cases, the establishment of natural enemies from the native environment may result in the reduction of the target species population to non-pest levels. I believe that the label classical, when referring to the type of biological control just described, has been adopted because the spectacular early successes in pest control, by using natural enemies, involved the importation of exotics, e.g. control of the cottony cushion scale, Icerya purchasi , in California with the predatory coccinellid Rodolia cardinalis imported from Australia in 1888; control of prickly pear, Opuntia spp., in Australia with the pyralid Cactoblastis cactorum imported from Argentina in the 1920s; the control of the coconut moth, Levuana iridescens, in the Fiji Islands with the tachinid fly Bessa remota imported from Malaya in 1925. Other than the importation of natural enemies for pest control, biological control involves the manipulation of resident natural enemies, native and exotic, to increase their regulating capabilities by providing favorable condi­ tions. This biological control tactic is much older than the one involving importation of species. For example, since ancient times, Chinese growers placed nests of the predatory ant Oecophila smaragdina in citrus trees to control various leaf-feeding insects (45).