Effects of various concentrations of Bacillus thuringiensis-corn leaf material on food utilization by Chilo partellus larvae of different ages

When herbivores feed on insect-resistant transgenic plants, food consumption and utilization are probably affected. Quantifying these parameters is of importance, because they may be associated with the performance of parasitoids, which are important antagonists of herbivorous pests. In this study, relative consumption rate (RCR), relative growth rate (RGR), approximate digestibility (AD), efficiency of conversion of digested food into body matter (ECD) and efficiency of conversion of ingested food into body matter (ECI) of Chilo partellus Swinhoe larvae (Lepidoptera: Crambidae) exposed to different concentrations of transgenic insect-resistant Bacillus thuringiensis-com (Bt-corn) tissue suspension, were investigated under laboratory conditions. For the control groups, different concentrations of control corn tissue suspension were used. In order to determine whether Bt effects were influenced by larval age, 4- and 17-day-old larvae were used. At all concentrations and for larvae of both ages, RGR, RCR, ECD and ECI values in the control were significantly higher than in the Bt group. Moreover, there was a gradual decrease in RCR, RGR and ECI values when Bt concentrations were increased. However, AD values at the lowest Bt concentration were significantly higher than in the control, whereas no significant differences between both groups could be detected at higher concentrations. In conclusion, the experiments showed that nutritional indices of herbivores exposed to transgenic insect-resistant plants could be quantified to determine the effects of these plants on target or non-target organisms. This could be one component in future evaluation of the effect of transgenic insect-resistant plants on the second and third trophic level.