Systematics of Insect Pathogenic Bacilli: Uses in Strain Identification and Isolation of Novel Pathogens

Abstract

Microbiological insecticides comprise micro-organisms which cause disease and ultimately death in insects. They are being used increasingly for control of agricultural pests and insect vectors of disease, either alone or in combination with chemicals in “lintegrated pest management”l programmes. The growing acceptance of microbial insecticides partly arises from disillusionment with chemical insecticides due to increasing resistance among target insects. Currently more than 500 insect and mite species have acquired resistance resulting in major agricultural and health problems. For example, mosquitoes resistant to most of the commonly used chemical insecticides have now emerged in many areas of the world (reviewed by Rawlins, 1989). One particularly well studied case involves resistance to organophosphates in the mosquito Culex quinquefasciatus which resulted from amplification of an esterase gene. The same mutation was detected in resistant mosquitoes from USA, India, Africa and south east Asia showing that a single mutation had arisen and the resistant population had rapidly become disseminated and established in different continents, presumably as a result of airline traffic (Raymond et al., 1991). Resistance to microbial insecticides, on the other hand, is currently very limited (McGaughey and Whalon, 1992; Hougard and Back, 1992) but unless strategic measures to avoid the problem are taken, it is anticipated that resistance will develop rapidly in target populations as they are used more intensively (McGaughey and Whalon; 1992; May, 1993).