Influence of Bt cotton on HaNPV isolates

Comparatively higher larval mortality was observed when the second instar larvae of H. armigera were fed on MECH-184Bt and MECH-162Bt without HaNPV spray. When different HaNPV isolates were sprayed on different cotton species including Bt with their non-Bt versions, there was an additive effect of Bt and NPV resulting in higher larval mortality on Bt plants, irrespective of the isolates used. Among the Bt cotton, the Mahyco Bt cotton hybrids registered higher mortality as compared to Rasi Bt hybrids. Again, among the Mahyco Bt hybrids, MECH-184Bt proved superior followed by MECH-162Bt and MECH-12Bt. Among the Rasi Bt hybrids, RCH-144Bt recorded higher % larval mortality followed by RCH-20Bt and RCH-2Bt. The number of larvae succumbed to viral infection was relatively more in case of Bt cotton hybrids. Among the Bt cotton, the larvae fed on the floral parts of MECH-184Bt encountered higher viral infection followed by MECH-162, MECH-12 and RCH-144Bt. Of the three species of cotton, G. barbedense var. B-82 harboured more number of virosed larvae. Irrespective of the cotton species used, Gulbarga, Coimbatore and Dharwad isolates recorded higher % of virosed larvae as compared to the other isolates.