Bacillus thuringiensis and insect pest management

Abstract

332 Bacillus thuringiensis, a motile, gram positive, rod shaped, spore forming soil bacterium characteristically synthesizes parasporal crystalline inclusions containing crystal (Cry) and cytolytic (Cyt) proteins possessing pesticidal properties against wide range of insect orders and nematodes. During vegetative growth stage, it also secretes insecticidal proteins, that is, vegetative insecticidal proteins (Vip) which hold insecticidal activity against Lepidopteran, Coleopteran and some Homopteran insects. Recently, a less well-characterized secretory protein which has no amino acid similarity with Vip has also been found to possess insecticidal activity against Coleopteran insect and termed as secreted insecticidal protein (Sip). Being ubiquitous, B. thuringiensis has been isolated from a diverse source of habitat which led to the discovery of various new strains. These strains are characterized into 71 serotypes and 85 subspecies based on flagellar-serotyping. Different strains produce different types of toxins, each of which affects a narrow taxonomic group of insects and this has led to the development of over 100 types of insecticides using natural and genetically engineered strains for topical application. In addition, the genes possessing insecticidal properties have been successfully transferred into cotton, corn, soybean, and rice, which have led to significant economic benefits. However, prolonged and continuous use of B. thuringiensis based bio-pesticide and transgenic crops have created the problem of insect resistance in only few insect species. In this chapter, we discuss about B. thuringiensis on the historical developments, prevalence and ecology, general characteristics, classification and nomenclature, various insecticidal proteins, and the topical and transgenic products. Finally, this chapter focuses on the developments in insect resistance management and the future prospects of B. thuringiensis in insect pest management.