Impact of transgenic Bt cotton on nutritional indices of spotted bollworm, Earias vittella (Fabricius) (Lepidoptera: Nolidae)

Abstract

The quality of food consumed by the insect is the key factor determining the utilization of food, thus having great impact on its survival, development, and longevity. Genetically modified plants with genes from soil inhabiting spore forming bacterium, Bacillus thuringiensis Berliner produces δ-endotoxin, which target the gut of insect, so food intake and its utilization are likely to be affected. Four Bt cotton hybrids, each with one of four events, viz. MRC 6301 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) were compared for nutritional indices of spotted bollworm, Earias vittella (Fabricius) (Lepidoptera: Nolidae) along their isogenic non-Bt genotypes. Various consumption and utilization indices, viz. consumption index (CI), relative growth rate (RGR), efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD) were worked out. The data show that all the Bt hybrids significantly reduced CI, RGR, ECI and ECD of 4th instar E. vittella larvae as compared to their isogenic non-Bt genotypes when fed on squares and bolls of 90, 120 and 150 days crop age. Further, the Bollgard II genotype MRC 7017 BG II was found to be more lethal and recorded significantly lower values for all the above given indices. Despite the fact that, the differences between Bt and their isogenic non-Bt genotypes decreased with increasing age of the crop but still Bt cotton hybrids were significantly inferior as insect food as compared to the non-Bt ones even at the later stages of the crop growth. The amount of Cry1Ac toxin in squares and bolls of Bt cotton had a significant negative correlation with food consumption and utilization indices of E. vittella larvae. The studies thus indicated that Bt toxin has a substantial impact on the nutritional performance of E. vittella.