For more than a decade, since before 2002, the American bollworm, Helicoverpa armigera, has unleashed terror in cotton fields by destroying more than 50% of cotton yields in India. Bollworm caterpillars had become resistant to all insecticides recommended for control and none of the chemicals worked, even when mixed as cocktails at doubled concentration. Investment, especially on insecticides, increased by leaps and bounds while yields had declined just as much. Within four years of its introduction, Bt cotton changed the story in India. Yields doubled. Insecticide use was reduced to half of the previous level. Several researchers estimated the net average gains from Bt cotton to be in the range of $76 to $250 per hectare.