Bacterial Pesticides

Bacterial Pesticides

Bacterial Pesticides
Several bacterial pathogens that have been used as insecticides include (a) endospore forming Bacillus and Clostridium species (b) non-endospore forming species of Pseudomonas, Enterobacter, Proteus, Serratia, Xenorhabdus. Of the potential bacterial pesticides, Bacillus thuringiensis has been most extensively studied.

Bacillus thuringiensis has been successfully tested against more than 140 insect species (Lepidoptera, Hymenoptera, Diptera and Coleoptera). At present, there are 12 groups of B. thuringiensis. All strains produce protein crystal inclusion bodies which act as endotoxin. They are toxic factors and are called parasporal bodies.

These crystals dissolve under alkaline condition. They are not soluble in water under neutral or acidic condition. The midgut contents of the caterpillar larvae (pests) are alkaline. On ingestion, the crystal dissolves in the midgut fluid and gets digested particularly by the proteolytic enzyme present in the midgut fluid. This digested protein crystal attacks the cementing substances which are present in the gut wall, thus loosening the epithelial gut wall which helps continuous diffusion of liquid from the gut into the blood making the blood of the insect highly alkaline and leading to gut paralysis. The parasporal bodies are highly toxic for caterpillars with an LD50 value of < 0.9 mg/ g of larvae.

The process of crystal synthesis and spore formation proceed simultaneously. The toxin production by a culture can be enhanced by controlling many factors.

Bacillus thuringiensis toxin genes have been introduced via recombinant DNA technology into the genome of plants or plant associated microorganisms.

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