Economic Benefits of Bt Maize Maize containing a transgenically expressed toxin originating from Bacillus thuringiensis (Bt maize) is planted across the United States to combat insect herbivory. Non-Bt Maize is also planted alongside Bt maize fields to provide refuges for the insects, which helps to prevent resistance to Bt maize from evolving. Hutchison et al. (p. 222 ; see the Perspective by Tabashnik ) analyzed how Bt maize affected the economic impact of the European corn borer moth in the midwestern United States, as well as its population dynamics. Larval density, a predictor of corn borer population size, has dropped in correlation with the percentage of Bt maize planted. In the highest Bt maize producing state, the positive effects of Bt maize in controlling insect herbivore populations extended to non-Bt maize. Furthermore, the decrease in insect populations demonstrated an overall economic benefit outweighing the overall extra costs associated with planting Bt maize.

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Materials and Methods Crop rotation influences yield and various soil properties due to changes in availability of nutrients and water, physical properties, and incidence of pests and weeds. A rotation crop study was started in 1979 to assess the effects of various crop sequences and nitrogen (N) fertilization for corn on crop yield. The rotations are continuous corn for grain and for silage, continuous soybean, several corn-soybean sequences with one to three corn crops for every soybean crop, and corn-corn-oats/alfalfa. Alfalfa is undersown with oats and only oats grain is harvested the first year. The tillage practices are chisel-plowing of cornstalks in the fall and field cultivation for all crops in the spring. The N treatments are 0, 80, 160, and 240 lb N/acre only for corn using granulated urea, which is spread in spring and incorporated into the soil. This report summarizes average grain yields of corn, soybean, and oats for the 28-year period (1979-2006) and the last four years when the 4-year rotations completed a cycle.