Season long bioefficacy of Bacillus thuringiensis (Bt) insecticidal protein against Helicoverpa armigera (Hubner), Earias vittella (Fabricius), Spodoptera litura (Fabricius) and Pectinophora gossypiella (Saunders) in Bt transgenic cotton RCH-2 BG-II (cry1Ac+cry2Ab) and RCH-2 Bt (cry1Ac) were investigated in Dharwad region of Karnataka, India, in 2007-08. The results showed that, the toxin content (larval mortality) in Bt cotton changed/ gradually declined as the advancement of the cropping season. Generally, insecticidal protein (larval mortality) levels were high during the early stage of the crop growth, gradually declined over time. Compared with RCH-2Bt, the expression (mortality) of cry1Ac+cry2Ab protein in RCH-2BG-II was significantly high during the whole cropping period
