Effect of Bacillus thuringiensis corn on natural enemies of the European corn borer

Since the commercialization of transgenic corn expressing endotoxin proteins from Bacillus thuringiensis Berliner genes (Bt corn), concern about the potential impact of this biotechnology-derived corn on nontarget organisms has been the focus of considerable attention. Several studies have been conducted in the laboratory and field to determine the impact of Bt corn on natural enemies (i.e., predators, parasitoids, and pathogens) of the European corn borer, Ostrinia nubilalis. The published literature is summarized and reviewed. Two types of experiments were conducted in Illinois to assess the impact of natural enemies on populations of first- and second- generation European corn borers. Small plot experiments were conducted in 1994 and 1995, and field-size studies were conducted in both Bt- and non-Bt cornfields during 1997 and 1998. In the small-plot trials, densities of predators in Bt and non-Bt corn plots were not significantly different during both years of the study. In the field-scale trials, corn type did not seem to affect the percentage of larvae parasitized by Macrocentrus grandii or the percentage of eggs and larvae infected by Nosema pyrausta. However, because densities of European corn borers in Bt corn were significantly lower than densities of European corn borers in non-Bt corn, densities of natural enemies were substantially reduced in Bt corn. Although reduced host density is predicted to coincidentally reduce parasitoid density, maintenance and effectiveness of natural enemies should be retained with establishment of non-Bt corn refuges for insect resistance management.