Association of the level of mosquito larvicidal activity with the growth &sporulation in Bacillus sphaericus H-5a5b strains

The role of growth and sporulation in the production of mosquito larvicidal factors in B. sphaericus H-5a5b strains was investigated using 6 strains t hat differed in their larvicidal activity. Among these, strain B64 produced maximum biomass (15.5 g/l by 29th h) while B45 and B85 yielded the least ( 12.8 g/l by 41st and 37th h respectively). Strains B43 and B42 reached the peak of viable cell count (4-6 x 10(10) cells/ml) 4 h earlier than B64 and 12 h earlier than the rest of the strains. Strains B42 and B43 produced hig her number of heat resistant spores (4 x 10(8) spores/ml), while strains B4 5 and B57 produced the lowest numbers (2-4 x 10(5) spores/ml). Mosquitocida l toxin synthesis was noticed as early as the 5th and 9th h in the cultures of the strains B42 and B64 respectively while in those of other strains it was detected by the 13th h or later. The results indicated that generally the highly and moderately toxic strains grew faster and sporulated better t han the poorly toxic ones.