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Abstract 1. Characterization of Bacillus thuringiensis (B.t) 1.1. History and application Microbial pesticides which were developed to avoid the toxicity associated with many chemical pesticides have been used for large scale pest control for more than three decades. The chief organism used for this purpose is Bacillus thuringiensts (B. t.). This bacteria was originally isolated from morbid silkworm moth, Bombyx mori, Lepidoptera larvae more than a centuty ago(l). Ten years later, a similar organism was isolated from Mediterranean flour moth, Ephestia kuehniella(2). In 1911 this bacteria was identified as the cause of death in flour moth larvae, Golleria melonella, (Lepidoptera) and gave this organism the name Bacillus thuringiensis/”. Later a B. t. strain isolated from the yellow mealworm beetle, Tenebrio molitor was found to be toxic to larvae of the Colorado beetle, Leptinotarsa decemlineata, (Coleoptera) and of other beetles as well(3). Today there are strain collections that contain several thousand B. t. isolates’i’”. Because they are highly effective against pests prominent in agriculture and forestry, many B. t. products are now used for pest control (Table 1.1). They act selectively against specific pests without harming beneficial organisms and are very safe for the user. Success of B.t. is due to the high efficacy of its insecticidal proteins, the existence of a diversity of proteins that are effective against a range of important pests; its relative safety to non target insect predators and parasites, its ease of mass production at relatively low cost, and its adaptability to conventional formulation and application technology. |