Novel Biopesticides by Author: M. V. Deshpande
By Author: M. V. Deshpande
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Chitin is regarded as a modified cellulose, of which the monomer is glucose. If the OH group on the second carbon atom in glucose is changed to an amino group then the corresponding polymer is called chitosan. Chitosan is strictly speaking, not a substance but is rather a family of partially modified chitin products. Chitosan is non-crystalline in nature. It occurs in the walls of a limited but medically important group of fungi. These fungi, named Zycomycetes are opportunistic invaders of man and can be major pathogens in burn wounds.
Israelensis was of immediate practical importance. Now the insecticidal preparations of this strain are being used all over the world for pest control. But then, how does the BT insecticide work? What is the secret of its efficiency? The sporulating cells of B. thuringiensis contain insecticidal crystal protein (Iep) which accounts for the commercial value of BT as a biopesticide. Actively growing cells lack the crystalline inclusions and thus are not toxic to insects. However, some strains exude small molecules of toxin which are appropriately enough, called exotoxins and 30 NOVEL BIOPESTICIDES Scientists have 12,145 cultures of different varieties of B.
Thus, although a potentially life- threatening viral infection has established itself in the insect's body, it goes on eating and damaging crops. Usually, 4- 6 days elapse between the time of ingestion of virus and the death of the host. Farmers therefore, are understandably unhappy about this delayed action biopesticide. There is another inherent drawback too. These viral preparations are not stable under the ----- - -- -- - .. - -- - - --.. BUGS AGAINST BUGS -- --- 25 The viral and bacterial control agents infect insects via their digestive tract while fungi make their entry into the host through the cuticle which is the superficial non-cellular layer covering plants and certain lower animals.