http://dragon.zoo.utoronto.ca/~jlm-gmf/T0201A/corn1.jpg

http://www.apsnet.org/online/feature/BtCorn/Images/healthy ear.JPG 

Here’s another extraordinary story of molecular crop enhancement. The damage done to corn by European corn borer is shown on the left. It’s most devastating effect is to hollow out the stalk so that the plant collapses and dies.  Moreover, as shown in the middle panels, fungi often follow the boring insects into the plant. Several biotechnology companies, the most familiar of which is Monsanto, transferred a gene from a soil bacterium call Bacillus thuringiensis -- abbreviated Bt -- to corn plants.  An ear on a transgenic Bt corn plant is shown on the right.  The bacterium itself has been used for insect control for many decades because it produces crystals of a protein that is toxic to certain kinds of insects, but not toxic to people or animals.  It has been sprayed from helicopters for the control of gypsy moths and organic farmers use it extensively. It is available  in garden stores under a number of brand labels, including Dipel.  It is considered so safe that the EPA hasn’t set what it calls a “tolerance” for it.  The EPA’s tolerance is the maximum level of a chemical, such as a pesticide or fungicide, that is considered safe for human health as a residue in food.  Bt corn is resistant to the corn borer because the plant itself expresses the bacterial protein.  This means that farmers don’t have to use chemical pesticides to control this pest, which is very difficult to control because of its boring life style.  The rapid adoption of Bt corn by farmers in many countries has dramatically reduced pesticide use. But there turned out to be an unexpected additional benefit of Bt corn.  Invading corn borers provide a path of infection for fungi, the most serious of which are fusarium ear rot and kernel rot (middle panels).  These fungi, which make the white stuff you see around the hole made by the borer, produces very toxic substances called fumonisins and aflatoxin, which cause serious neurological diseases and death in animals and people.  The use of Bt corn dramatically reduces the incidence of contamination by such fungal toxins.