While cotton may not be a food, it's such a ubiquitous crop that it's worth mentioning. China produces more cotton than any country in the world and for more than 15 years, it has been genetically modifying its cotton to help combat the effects of the bollworm. The boll is the protective shell that the soft cotton ball grows inside of, and it's at risk because of the bollworm's persistence.
With the advent of "Bt cotton," China, courtesy of Monsanto, the controversial biotech company headquartered in Missouri, has been able to cut back on spraying pesticides. The good news is that studies found a sharp reduction in bollworm infestation despite the lower amount of pesticides. It also increases overall yield. The bad news is that Bacillus thuringiensis, the specific pesticide that's actually bred into the cotton, isn't effective on a formerly lesser pest, the mirid bug. And what's worse, now that the cotton is infested, the mirid is becoming a problem for other nearby crops.