Matin Qaim and David Zilberman

Hitherto applications of genetically modified (GM) crops in the United States, China, and Argentina have led to significant reductions in the use of chemical pesticides, but, in most cases, yield increases have been rather small. Although pesticide savings bring about important economic and environmental gains, it has often been argued that GM crops have little to offer to the poorest countries where local agricultural output needs to be increased on a limited amount of farmland. We argue that this generalization based on partial data is false. By using the example of Bt cotton in India, we suggest that currently-existing GM crops can have significant yield effects, which are most likely to occur in the developing world, especially in the tropics and sub-tropics. The evidence in India supports a general principle that a pest-control strategy, in this case biotechnology, has a strong yield effect in locations where pest damage is substantial and use of alternative control agents is constrained.

Bt cotton provides a fairly high degree of resistance to the American bollworm (Helicoverpa armigera), the major insect pest in India. The technology was developed by Monsanto and was introduced into several Indian hybrids in collaboration with the Maharashtra Hybrid Seed Company. Field trials with these Bt hybrids have been carried out since 1997 and, for the 2002/03 growing season, the technology was commercially approved by the Indian authorities. Its performance during the first commercial season in India is hotly disputed among biotechnology advocates and opponents, but an independent scientific assessment has not been conducted thus far.

For our analysis, we used data from on-farm field trials that were carried out during the 2001/02 growing season as part of the regulatory procedure. On 157 farms in three different states, Bt cotton hybrids were planted next to an isogenic line without the Bt gene and a local hybrid commonly grown in the particular district. All three plots were managed by the farmers themselves, following customary practices. Apart from official data that were collected by local researchers for biosafety evaluation, we used our own questionnaire to obtain details on input-output relationships from participating farmers.

While there was no significant difference in the number of sprays against sucking pests, Bt hybrids were sprayed three times less often against bollworms than the conventional hybrids. On average, insecticide amounts on Bt cotton plots were reduced by almost 70%, which is consistent with studies from other countries. The difference in India, however, is that use of Bt cotton also leads to a significant yield effect. During the field trials, average yields of Bt hybrids exceeded those of non-Bt counterparts and local checks by 80% and 87%, respectively.

Bt is a pest-control technology, so rather than an increase in the genetic yield potential, these effects have to be interpreted as avoided crop losses. Figure 1 confirms that, under Indian conditions, bollworms have a high destructive capacity which is not well controlled in conventional cotton. At average pesticide amounts of 1.6 kg/ha (active ingredients) on the conventional trial plots, crop damage in 2001/02 was about 60%. Bt does not completely eliminate pest-related yield losses. Yet, to achieve the same level of damage control without the technology would require a triplication of currently used pesticide quantities.

Figure 1: Insecticide use and crop losses with and without Bt technology

2001/02 was a season with high bollworm pressure in India, so that average yield effects will be somewhat lower in years with fewer pest problems. Moreover, although the trials were managed by farmers, experimental results cannot simply be extrapolated to commercial agriculture. But even when discounting for these aspects, yield advantages of Bt cotton will remain bigger in India than in the United States or China.

Analysis of factors influencing yield impacts of new, effective pest control technologies suggests that they depend on local pest pressure, availability of alternatives for pest control, and farmers' adoption of these alternatives. Generally, pest pressure in tropical and sub-tropical regions is higher than in temperate zones, while pesticide-use intensities are much lower, due to technical and economic constraints. In India, pesticides are available on local markets, but their effectiveness is limited because bollworms have developed resistance to many of the common products. Furthermore, small-scale cotton producers are often credit-constrained and do not have access to chemicals at the right point in time.

Given these linkages, we have a theoretical base to suggest that the case of Bt cotton in India might be more representative of GM crop impacts in developing countries than previous examples. Almost all GM crop technologies were initiated by commercial firms in the industrialized world, targeting the needs of farmers who are able to pay for them. Some varieties were transferred to the commercial sectors of Latin America and China, where agroecological conditions and pesticide application rates are similar. In all cases, yield effects have been low to medium, while there have been significant gains from pesticide substitution.

However, with careful adaptation and effective regulation, these same technologies can also be introduced to other developing-country regions, where yield effects will be more pronounced. Pest-resistant GM crops are easy to manage at the farm level, and they could substantially reduce current gaps between attainable and actual yields, especially in smallholder farming systems. Preliminary evidence from Indonesia and South Africa is in line with this hypothesis. Agricultural biotechnology offers many more applications for developing countries beyond pest control, but we show that the GM crops developed thus far can already have significant impacts. It is a major policy challenge to invest more in public research and address the existing institutional constraints, so that promising biotechnologies can reach the poor at affordable prices on a larger scale.


Qaim M and Zilberman D. 2003. Yield effects of genetically modified crops in developing countries. Science 299: 900-902.

Matin Qaim
Ctr for Dev Res (ZEF)
Univ of Bonn, Germany
David Zilberman
Ag and Resource Economics
Univ of California at Berkeley