Comparative study on oviposition and larval preference of spotted bollworm, Earias vittella on Bt and non-Bt cotton.

Oviposition and larval preference of spotted bollworm, Earias vittella (Fabricius) was assessed on four transgenic Bt cotton hybrids, viz. MRC 6304 Bt (cry1Ac gene), JKCH 1947 Bt (modified cry1Ac gene), NCEH 6R Bt (cry1Ab/cry1Ac fused gene) and MRC 7017 BG II (cry1Ac and cry2Ab genes) in comparison to the respective isogenic cotton. The results showed that Bt toxin did not deter oviposition preference of E. vittella moths as there was no significant difference in the number of eggs laid on squares/bolls of Bt and non-Bt cotton hybrids, across different crop growth stages. There was also no behavioral change in larval preference with respect to selecting non-Bt cotton in comparison to Bt cotton. Floral bodies from Bt and the respective isogenic cotton genotypes were equally preferred by both first and third instar larvae after 24 hrs indicating that initial selection was independent of susceptibility to Bt toxin. However, E. vittella larvae showed significant difference in preference for different cotton genotypes. Studies on the relative preference indicated that third instar larvae had greater preference for bolls (7.29-7.50%) than for the squares (5.0-5.21%) and reverse was true for the first instar larvae which showed greater preference for squares (7.08-7.29%) than for the bolls (5.21-5.42%), in a multiple-choice test. It may be concluded that oviposition and larval preference of E. vittella did not differ significantly between Bt and isogenic non-Bt cotton genotypes.