GM Crops? Ecological Effects?
7 Jun, 2007 08:00 pm
Researchers at Santa Clara University in California have investigated the effects of genetically modified crops on insects. The study is published in the June, 8 issue of Science. Interview with Michelle Marvier, lead author of the report.
In general, the number of invertebrates that are not the target of GM crops is higher in fields with BT crops (genetically modified crops produce the insecticide Bt) rather than in fields where crops are sprayed with pesticides. So pesticides have a greater effect on these non target invertebrate populations (butterflies, honeybees...) than does BT cotton or BT maize.
What conclusion can you draw from this study about the environmental effects of genetically modified crops?
The most important conclusion is probably that it depends on which type of comparison you do. If you compare BT crops to crops which are not sprayed with any type of pesticides, you see a reduction of invertebrates being cut by the BT crops. But if you compare the same BT crops to crops that are spayed with pesticides, BT crops can be looking pretty good. What really matters is the comparison we decide to do and choosing what should be an appropriate comparison has been somewhat controversial up to this point.
BT maize has been widely adopted in the United States. In that case the appropriate comparison may be with maize that is not sprayed with pesticides because most of the maize we grow, even what we call sweet corns that is used for barbecues and so forth, is corn grown for conserves or to cows. On that type of corn we donít tend to spray a lot of pesticide. So the appropriate comparison is with corn that is not sprayed with pesticides, which makes BT not look so good.
You've drawn together results from multiple studies. How did you proceed?
This is called meta-analysis. We gathered all the studies that we could find or had performed looking at the effects of BT cotton and BT maize in the fields. From each study we drawn the details about the method and as much information as we could about the different results. Then we used meta-analysis to combine results across these studies. Thatís very important because each study by itself tends to have very few replicates and by pulling them all together we can have a better stance on the effects of BT crops on the environment.
Dr. Michelle Marvier is a researcher in the Department of Biology & Environmental Studies Institute at Santa Clara University
Interview by: Clementine Fullias