Biological Control
The term 'biological control' is usually interpreted as the action of predators, parasites and pathogens in maintaining the population density of another organism at a lower level than would occur in their absence. In an applied sense, however, biological control is the study and utilisation of natural enemies (parasites, predators and pathogens) for the regulation of host population densities to reduce the damage caused by noxious organisms.
The modern history of biological control dates from the spectacular control of the cottony cushion scale (Icerya purchasi) by the introduced vedalia beetle in citrus plantations in California in 1888. Yet the value of ladybirds in destroying aphids in English gardens was well noted at the beginning of 19th Century. Pope (1981) studied another important Australian species Rhyzobius ventralis (Erichson), used as a biological control agent against various scales, mostly Eriococcus and Lecanium in California, Hawaii, New Zealand and other places with mixtures of success and failure. His detailed taxonomic and ecological analyses of these introductions showed that two morphologically similar but biologically very different species (Richards 1981) were involved at various stages of introductions causing their common failure.
Smith, Papacek and Smith (1995) described integrated pest management (IPM) procedures applied in the citrus orchards in south-eastern Queensland to control citrus snow scale Unaspis citri (Comstock). Parasitoids and introduced species of ladybirds Chilocorus circumdatus Gyllenhal provided control of the scale within two years of establishment. Obrycki and Kring (1998) reviewed a role of coccinellids in biological control and concluded that they will continue to play important role in naturally occurring and human assisted biological control, and they will be considered as possible natural enemies for importation whenever a homopteran pest invades a new region. They concluded the use of insecticides being the single most detrimental factor to the survival of coccinellids in agroecosystems and advocated use of conservation techniques to enhance the effectiveness of naturally occurring and released coccinellids.