Production & formulation of Bacillus thuringiensis var. israelensis & B. sphaericus 1593.

Three fermentation media each for bulk growth of B. thuringiensis var. israelensis and B. sphaericus 1593 were formulated using defatted groundnut cake (Arachis hypogea) as the first nitrogen source and gram flour (Cicer arientinum), soy bean (Glycine max) and defatted milk powder as the second nitrogen source. Medium containing gram flour showed highest toxicity (14.45 micrograms/l) in case of B. thuringiensis var. israelensis whereas medium containing milk powder was found to be highly toxic with B. sphaericus 1593 (51.39 micrograms/l). Sustained release floating pellet formulations of B. thuringiensis var. israelensis and B. sphaericus 1593 exhibited toxicity of 77 per cent and above for 42 days at a dose of 500 micrograms/l for 4th instar larvae of Culex pipiens quinquefasciatus Say.

Growth & toxicity of Bacillus thuringiensis var israelensis.

Chemically defined media containing glutamic acid, glutamine and aspartic acid at a 20 mM concentration individually supported abundant growth and sporulation of Bacillus thuringiensis var israelensis. The parasporal crystals produced in these media were toxic to fourth instar larvae of Culex pipiens quinquefasciatus Say. The medium containing 20 mM of glutamine induced early sporulation of B. thuringiensis var israelensis. An LC50 value of 3.92 micrograms/l was obtained. Calcium alginate and agar agar immobilized formulations of Bacillus thuringiensis var israelensis exhibited toxicity of 90 per cent and above to C. pipiens quinquefasciatus Say larvae, over a period of 90 days.