Effect of Bt maize on the plant-aphid-parasitoid tritrophic relationships

The effect of Bt maize on aphid parasitism and the aphid-parasitoid complex was measured in field conditions on three transgenic varieties, two derived from Event MON810 and one from Bt176, and their near-isogenics in a two-year study. No differences in aphid abundance were found between Bt maize varieties and their near-isogenics. Differences within Bt and within near-isogenic varieties were found, but only in one year. Differences in aphid abundance were probably better accounted for the variety background and year conditions than by the transgenesis or Event. Lysiphlebus testaceipes (Cresson), Lipolexis gracilis Forster (Hymenoptera, Braconidae, Aphidiinae) and Aphelinus sp. (Hymenoptera, Aphelinidae) were the prevalent parasitoids. Bt maize did not alter the aphid-parasitoid associations and had no effect on the aphid parasitism and hyperparasitism rates. The results suggest that Bt maize has no negative impact on second, third and fourth levels of the trophic relationships studied.