Evaluation of the Effects of BT-Maize on Non-Target Insects Using a Demographic Approach

An experiment on life-table of the aphid on Bt-maize and isoline was performed. No significant differences were found between treatments. Differences in aphid performance were the lower adult and total longevity on the second generation, and the opposite trend of the pre-reproductive time that increased from the first to the second generation on isoline and decreased on Bt-maize. None of the demographic parameters analyzed showed significant differences. LTREs showed that this trend could be ascribed to a higher fecundity of young adult aphids of the second generation, probably connected to the lower pre-reproductive time. These differences could be the result of differences in chemical constituents. Analyses of secondary metabolites showed significant reduction of free polyphenols in Bt-maize. The experiment with the coccinellid H. variegata were performed evaluating the effects due to eating Cry1Ab toxin in maize pollen. No significant differences were found between GM and near-isogenic maize in all the parameter studied. Even if no significant, the reduced λ of H. variegata feeding on Bt-maize pollen, caused a population delay of 28 days. LTRE decomposition showed a lower egg and larval survival in the offspring of Bt pollen fed H. variegata, all contributing most on λ reduction. A bioassays were carried out in the greenhouse to assess the population-level responses of the coccinellid H. variegata, feeding on aphids reared on Bt-Maize and near-isogenic plants in a more realistic condition respect to laboratory trials. No differences in the mean number of eggs, larvae, pupae, and adults of H. variegata between Bt-maize and near-isogenic line. A higher number of pupae was found a week early in Bt-maize. No differences observed in H. variegata population growth rates between treatments. Using LTRE decomposition, the effect of Bt-maize exposition on λ have been decomposed into contributions arising from the effect on each stage-specific parameter.