Because Bt cotton and Bt corn provide pest protection in the plant( a gene is expressed that is toxic to lepidoptera species of insects) there is no need for the less effective broad spectrum application of insecticides. As a result only insects that feed directly on the plant are affected. This is a great stride in protecting diversity and beneficial insect populations. In addition it reduces worker exposure to pesticides (with regards to both conventional and organic production). For example, in China, 400-500 deaths per year are attributed to pesticide poisoning. Since the introduction of Bt crops in China, pesticide applications have decreased by 75%.
The Bt plant genetics essentially displace the manufactured synthetics. According to research from Dr. Roger Leonard at the LSU Agricultural center and Dr. Ronald Smith at Auburn University, 1.04 million fewer pounds of insecticide are applied each year as a result of the reliance on Bt genetics in cotton alone. As a result about 2 million gallons of fuel are saved each year from decreased manufacturing and distribution of chemical pesticides. In addition, 2.41 million gallons of fuel and 93.7 million gallons of water are saved on the farm from fewer insecticide applications.
Sources: Dr. Roger Leonard, LSU Agricultural Center. Dr. Ronald Smith, Auburn University. Gregory Conko “The Benefits of Biotech” Regulation Spring 2003.
Gerald C. Nelson Genetically Modified Organisms in Agriculture: Economics and Politics San Diego Academic Press 2001.