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

Abstract

Numerous lines of genetically modified rice expressing cry genes fromBacillus thuringiensis (Bt) have been shown to confer resistanceto lepidopterous pests of rice (stem borers and leaffolders) underlaboratory and field conditions. Stem borers and leaffolders arechronic pests that generally do not cause high yield losses on anindividual field basis, but their feeding damage results in substantialcumulative yield losses in rice growing countries because of theirwidespread occurrence. The adoption of Bt rice will therefore providemodest but consistent yield increases. Understanding farmer decision-makingpractices will be necessary to achieve the full potential of Bt riceto decrease insecticide use. No negative effects of Bt rice on predators,parasitoids, non-lepidopterous herbivores, or soil invertebrateshave been detected, except when natural enemies are fed Bt-intoxicatedprey. Effects of Bt rice on soil microorganisms have been observedbut have not been shown to have negative consequences for soil health.Despite the fact that outcrossing of Bt genes to wild and weedy ricewill almost certainly occur, possible consequences of outcrossinghave received little study. There is a high risk of development ofpest resistance to Bt rice, because of the challenge of implementingresistance management programs for millions of small farmers andbecause the major target pests (the stem borers Scirpophaga incertulasand Chilo suppressalis) do not have important alternative hosts thatcan provide natural refuges. As of December 2007, Bt rice had notbeen commercialized in any country.