Department of Agricultural Entomology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur-741252, Nadia, West Bengal, (India).
1A part of approved Ph.D. thesis submitted by A. Pramanik to Bidhan Chandra Krishi Viswavidyalaya, Kalyani, West Bengal, (India).
The persistent toxicity of Bacillus thuringiensis var. kurstaki (Delfin WG, 53 × 109 SU/kg) was studied against the third instar larvae of Spilosoma obliqua Walker on different host plants under field condition. The persistence of B.t.k. degraded very fast within 4 days after spraying as was evident from 100.00 to 10.00%, 100.00 to 16.67%, 100.00 to 13.33%, and 93.33 to 6.66% larval mortality on mung, red gram, rice bean and jute, respectively. The biocide persisted little longer on rice bean and red gram as compared to other two crops. According to their PT values, the order of persistent toxicity of B.t.k. on different host plants was rice bean (356.66) > red gram (333.34) > mung (309.99) > jute (259.99).
