Bt cotton, developed to resist bollworm attack, can have significant economic and environmental benefits, according to a three-year study of hundreds of Chinese smallholder farmers. The study, carried out by collaborators from China and the USA, also revealed that growing Bt cotton can have a positive impact on human health. The main benefits to farmers from using Bt varieties were increased crop yield and reductions in the amount of pesticide used. As well as lower input costs, growers reported fewer pesticide-related illnesses associated with growing Bt cotton, as compared with the non-Bt varieties.

While the authors describe greater chemical use in some areas of China growing Bt cotton, they found no evidence of an associated increase in pesticide resistance within the bollworm population. They believe that the transient increase in pesticide use was due either to changes in pest pressure, or the fact that some farmers were sowing seed saved from the previous year. This could have reduced the effectiveness of the resistant crop variety. Economic theory has correctly predicted that increased supply would result in lower market prices for cotton growers. The authors conclude, however, that current prices still offer considerable economic gains for farmers growing the Bt varieties.