Evaluation of Bt Cotton Hybrids in Comparison with Non Bt Cotton Against First Instar Larve of Spodoptera litura

The lab performance of certain released Bt cotton hybrids for their effect on Spodoptera litura were evaluated in comparison with non Btcotton. Studies were conducted at Insectary Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore during 2008–2009 to study the effect of transgenic Bt cotton hybrids viz., one Bt bunny, Seven Bollgard II (cry 1 Ac + cry 2 Ab genes) viz., RCH 2 Bt, RCH 515 Bt, RCH 596 Bt BG II, RCH 530 Bt, RCH 134 Bt and RCH 533 Bt and two non Bt cotton viz., Non Bt bunny and RCH 2 non Bt cotton against cotton leaf worm, S. litura first instar larva. Four plant parts viz., young green bolls, top fully opened young leaves, middle leaves and squares were tested. Among the Bt cotton hybrids and non Bt cotton evaluated, RCH 2 Bt young green bolls showed highest per cent mortality (72.7%), top fully opened young leaves (61.67%), squares (61.0%) and middle leaves (45.8%) observed at 168 hours after the treatments (HAT) followed by green bolls, top fully opened young leaves, squares and middle leaves of RCH 515 Bt that recorded 71.7, 60.7, 60.01 and 43.3 per cent mortality, respectively after 168 HAT when compared to green bolls, top fully opened leaves, squares and middle leaves of RCH 2 non Bt cotton which recorded 15.0, 11.7, 10.7 and 8.3 per cent mortality, respectively after 168 HAT.