Oviposition of European corn borer (Lepidoptera:Pyralidae) and impact of natural enemy populations in transgenic versus isogenic corn

In a 1994 field experiment, oviposition, predation, and parasitism of the European corn borer, Ostrinia nubilalis (Hubner), were recorded in transgenic and isogenic corn, Zea mays L. Plots of plants expressing the CrylA(b) protein of Bacillus thuringiensis Kurstaki and plots of isogenic plants both had end-generation O. nubilalis egg mass densities of approximate to 1.1 per plant, indicating a lack of antixenosis by transgenic plants. Distribution and size of egg masses on plants also was unaffected by corn type. Size of plants was the same in both treatments. Level of egg mass predation were 24.75 and 19.35%, respectively, but not significantly different between the transgenic and isogenic plots. Parasitism of egg masses was not significantly different between transgenic and isogenic plots, and was low at 6.31 and 4.41%, respectively. Percentage of eggs within masses which hatched was 10.2% lower in transgenic than in isogenic plots. However, neither predation, parasitism, or sloughing of eggs from plants were significantly different between the 2 treatments. Densities of O. nubilalis predators were not different between the 2 treatments throughout the O. nubilalis oviposition period. Parasitism of O. nubilalis larvae by Eriborus terebrans (Gravenhorst) and Macrocentrus grandii Goidanich was not significantly different between plots and ranged from 2.4 to 7.0%. Although most differences between transgenic and isogenic plants were nonsignificant, all observed differences in natural enemy population parameters under our conditions were in the direction opposite to that expected if transgenic plants had an adverse impact.