The food utilization efficiency of Earias vittella (Fab.) on squares of Bt cotton genotypes was greatly reduced compared to non-Bt genotypes. Second generation Bt cotton genotypes were  found to be superior over BG-I hybrids. With statistical advantage of 0.70 less CI in second generation Bt hybrids compared to non Bt, the food utilization efficacy was found to be significantly reduced, Bt hybrids were having 0.61 less CI and found superior over Non Bt. Low growth rate was noticed in BG-II (0.10-0.12 mg/day) followed by RCH-2 BG-I (0.18-0.21 mg/day). Similar trend was followed in efficacy of conversion of ingested food (ECI), approximate digestibility (AD/AE) and efficacy of conversion of digested food ECD (%).