ABSTRACT
Genetically modified (GM) maize is one of the 11 GM crops grown commercially in United States and Canada. Maize varieties resistant to glyphosate herbicides have been produced. There are also maize hybrids with tolerance to imidazoline herbicides marketed by Pioneer Hi-Breed under the trademark “Clearfield” but in these, the herbicide-tolerance trait was bred without the use of genetic engineering. The non-Bacillus thuringiensis (Bt) pesticide status of the refuges is being compromised by wind-borne pollen drifting into the non-Bt maize fields. Maize is a cross – pollinating crop in which most pollination results from pollen dispersed by wind and gravity. Traits that have been engineered into maize include resistance to herbicides and resistance to insect pests, the latter being achieved by incorporation of a gene that codes for the Bt toxin. The density of Bt maize pollen that overlays milkweed leaves in the environment rarely comes close to the levels needed to harm monarch butterflies.
