from gizmodo.com: Well that certainly didn't take very long. According to a study published Monday, the Western Corn Rootworm (actually a beetle larvae) has already developed a resistance to not one but two strains of genetically modified corn thanks to the over-reliance and improper implementation of the crops by farmers in Iowa.
Researchers first discovered that the worms were growing resistant to the Cry3Bb1 strain of Bt Corn back in 2009. Two years later, researchers subsequently found the worms chomping on a second strain of Bt Corn, mCry3A, in an adjacent field—spurring fears that the worms may have developed cross-resistance to both strains due to their close proximity to one another.
Turns out both Cry3Bb1 and mCry3A when managed incorrectly don't produce enough toxin to kill the largest and healthiest of rootworms, which quickly led the population to select for larger, more robust (and therefore more toxin-resistant) specimens. So now Iowa has bigger, more destructive rootworms that can shrug off the effects Bt Corn's toxins. Nature, it seems, has indeed found a way.