ABSTRACT
Insecticidal microorganisms were first reported in the 19th century in an unfavorable light when diseases of honey bees and silk moths were traced to microbial origin. 1 Among the biological pesticides, bacteria are the most potential and successful group of organisms identified so far for the effective control of insect pests and vectors of diseases that have rapidly become resistant to chemical pesticides. Insecticidal bacteria may be broadly classified as true pathogens, opportunistic or facultative pathogens, and food poisoning organisms. Davidson 2 considers those microbes “which invade host tissue and overgrow the host” as the true pathogens and those “which kill the host by means of toxins produced outside the host” as food poisoning organisms. The best examples of bacterial insecticides that have been investigated for almost 85 years are the members of the genus Bacillus. Among these organisms, the most commonly used and intensively investigated insect pathogens are Bacillus thuringiensis and Bacillus sphaericus. The emphasis of this review is molecular biology; therefore, we shall necessarily limit our discussion to these two organisms.
