The Billion Dollar Bug
The rootworm was given the nickname "Billion Dollar Bug" because of the large amount of crop yield lost caused by it (Gassmann 2012). To combat this North American pest corn was genetically engineered to contain the DNA of the bacteria, Bacillus
thuringiensis
(Bt). The new DNA allowed the corn plant to now release Bt toxin to kill rootworms This toxin was at first widely successful in deterring crop damage by rootworm; however, Bt toxin must be exposed to this pest at high enough levels to kill all rootworms in contact with it (Gassmann, 2012). Otherwise the rootworms not killed will have genes that protect them somewhat from the toxin (Gassmann, 2012). As they bred and pass on their genes, their offspring will also be selected for this protection; resulting, after many generations, in a tolerance or resistance to the Bt toxin (Gassmann, 2012). The high levels required to prevent this are thought to be twenty-five times more than what is needed to kill 99.99% of rootworms (Gassmann, 2012). There were four populations of rootworm that exhibited resistance in Iowa by as early as 2009 (Gassmann, 2012).
To learn about what is currently being done to combat resistance:
Picture courtesy of: http://www.ars.usda.gov/is/graphics/photos/oct09/k1289-17.htm