Author(s):

Murali Krishna T, Devaki K, Swarna B, Abhijit N and Naresh M

Abstract: A total of 203 Bacillus thuringiensis isolates were collected from soil samples native to southern zone of Andhra Pradesh distributing in Chittoor, Kadapa and Nellore districts. These isolates were tested for their efficacy against third instar Spodoptera litura in laboratory bioassays with leaf dip method. Out of 203 isolates 21 isolates (C44, C33, C59, C63, C79, C92, C97, C105, C134, C212, K18, N3, N30, N44, N48, N58, N115, F287, F468, F493 and F504) were observed with a mortality of more than 75 per cent against third instar S. litura larvae. These isolates were further tested for fixing the lethal doses to kill 50 per cent third instar S. litura larval population. Among the 21 isolates, the LC₅₀ values were in the range of 9.59´ 10⁴ to 1.88´ 10⁶ and in HD-1 lowest LC₅₀ of 9.56 ´ 10⁴ followed by 9.76 ´10⁴ in F493 and N30 with 1.90 ´ 10⁵.Whereas, highest lethal concentration to kill 50 per cent S. litura was 1.88 ´ 10⁶ spores ml^-1 in C212. Lowest time to kill 50 per cent was noticed in HD-1 (61.99 h), followed by F493 (78.52 h) and F468 (74.28h) and N115 (88.68h). Among the 21 isolates, F493, N30, F468, N115 can be used to develop Bt based biopesticide formulations for S.litura control.

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