Laboratory evaluation of native Bacillus thuringiensis isolates against second and third instar Helicoverpa armigera ( Hubner ) larvae

Second instar Helicoverpa armigera larvae were treated with B.t. strains isolated from soil samples and recorded mortality in the range of 16.67% to 94.44%. Maximum mortality was observed in reference strain HD1 which was on par with the B.t. strain 281 isolated from North Telangana Zone. There was no mortality of larvae in the untreated control. B.t. isolates 122 and 22 recorded 83.33% mortality. Lowest mortality was recorded in B.t. strains 252 and 261 isolated from North Coastal Zone. 50% of B.t. strains recorded more than 50% mortality. Among six B.t. strains isolated from bacteria infected silkworms except B.t. strain 432, remaining other B.t. strains showed more than 50% mortality. Third instar larvae of H. armigera were treated with native B.t. strains isolated from soil samples collected in different zones of A.P. and mortality was recorded in the range of 5.56% (B.t. strain 261) to 83.33% (HD1). Highest mortality was recorded in B.t. strain HD1 which was on par with the B.t. strains 22 and B.t strains 44, 87, 122. No larval mortality was observed in the control. 35% of the B.t. strains showed more than 50% mortality. Among six native B.t. strains isolated from bacteria infected silkworms, 50% mortality was recorded in B.t. strains 431, 434, 440 and 447. Forty B.t. strains (12, 22, 25, 44, 53, 58, 65, 71, 83, 87, 91, 95, 106, 122, 139, 153, 169, 175, 182, 193, 206, 224, 229, 242, 281, 291, 299, 307, 317, 341, 351, 372, 376, 408, 422, 424, 431, 434, 440 and 447) recorded more than 50% mortality against second and third instar H. armigera.

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