Bt Rice in Asia: Potential Benefits, Impact, and Sustainability

Abstract

Numerous lines of genetically modified rice expressing cry genes from Bacillus thuringiensis (Bt) have been shown to confer resistance to lepidopterous pests of rice (stem borers and leaffolders) under laboratory and field conditions. Stem borers and leaffolders are chronic pests that generally do not cause high yield losses on an individual field basis, but their feeding damage results in substantial cumulative yield losses in rice growing countries because of their widespread occurrence. The adoption of Bt rice will therefore provide modest but consistent yield increases. Understanding farmer decision-making practices will be necessary to achieve the full potential of Bt rice to decrease insecticide use. No negative effects of Bt rice on predators, parasitoids, non-lepidopterous herbivores, or soil invertebrates have been detected, except when natural enemies are fed Bt-intoxicated prey. Effects of Bt rice on soil microorganisms have been observed but have not been shown to have negative consequences for soil health. Despite the fact that outcrossing of Bt genes to wild and weedy rice will almost certainly occur, possible consequences of outcrossing have received little study. There is a high risk of development of pest resistance to Bt rice, because of the challenge of implementing resistance management programs for millions of small farmers and because the major target pests (the stem borers Scirpophaga incertulas and Chilo suppressalis) do not have important alternative hosts that can provide natural refuges. As of December 2007, Bt rice had not been commercialized in any country.