Types of entomopathogenic bacteria

• Some are obligate but majority is facultative and a few are potential pathogens.
• Some are very virulent bacterial species ( thuriengiensis).
• Most of the insect pathogenic bacteria occur in the families Bacilliaceae, Pesudomonadaceae, Enterobacteriaceae, and Streptococcaceae.
• Members of Bacillaceae, particularly thuriengiensis and B. popiliae, have received considerable attention as microbial control agents.

Mode of action of entomopathogenic bacteria

• They enter mostly through mouth and digestive tract. Also enter an insect by means of parasitoids and predators.
• Most commercial Bt products contain the insecticidal crystal protein (endotoxin) and spores, but some contain only the toxin component.
• Most of the bacterium including Bt, endotoxin is nontoxic to warm blooded animals.
• Bacterial spore is sprayed over the foliage and the insect ingests the spores.
• Bacterial insecticides must be eaten by target insects to be effective, they are not contact poisons.
• When Bt is ingested by a susceptible insect, the protein toxin is activated by alkaline conditions and enzyme activity in the insect’s gut.
• If the activated toxin attaches specific receptor sites, it paralyses and destroys the cells of gut wall, allowing the gut contents to enter the insect’s body cavity.
• Ingested Bt spores releases the endotoxins which causes the insect to stop feeding after a few hours and insect die within a day or two.
• Bacterial based mycopesticides are inundatively applied.
• Bt are one of the few so-called insecticides that are acceptable for management of insects in organic farming systems.
• Bacterium toxins are inserted into several crops using genetic engineering technology.

Limitations:

• Ultraviolet light in sunlight kills the bacterial spores.
• Like synthetic pesticides, the target pests can develop resistance to Bt.
• House flies and Drosophila developed resistance to the exotoxin.
• Tobacco bud worm, Heliothis viresens, has developed resistance to the endotoxin.