"We are reporting on cotton, but the results are easily transferable to food crops since the type of pest damage they would sustain would be the same," said Matin Qaim, assistant professor of agricultural and development economics at the University of Bonn's Center for Development Research and the study's lead author. "With populations in developing countries growing exponentially, and available farmland stagnating, there is an urgent need to find ways to increase crop yields on the land that is available."

While transgenic crops have been shown to reduce the use of certain chemical pesticides, they have not been known to substantially increase crop yields in the countries where they have been grown. For example, the yield gains of insect-resistant cotton crops in the United States and China average less than 10 percent. Bioengineered corn and soybeans have even less impressive gains, and in some cases, the yield effects are negative.

Why the difference in India? The answer seems to be that the region suffers from a significantly higher pressure of crop-destroying pests, and that there has not been a widespread adoption of chemical pesticides in India to control crop damage. Transgenic crops would likely have greater potential to increase yields in such regions, said the authors.

"The large scale applications of genetically modified crops in the United States or China are not truly representative of what would happen if the crops were grown in the small farm sectors of poor countries in tropical and subtropical climates," said Qaim, who conducted the research while he was a post-doctoral fellow at UC Berkeley's Department of Agricultural & Resource Economics, which is within the College of Natural Resources. "The results we see in India are much more representative of what would happen if transgenic crops were used in sub-Saharan Africa or Southeast Asia."

The temperature and humidity of tropical regions produce ripe conditions for insects that munch on crops. Absent the regular use of pesticides, crops in those regions are defenseless against pests.

Qaim said the reason China has not seen significant yield gains in its transgenic crops is that the country has long had a well-developed infrastructure to support pesticide use for its farmers. Since pesticide sprays are widely used for non-transgenic crops, the loss of yield is not as severe.

But for the majority of developing nations, the high cost of pesticides makes them too risky an investment for small, non-commercial farmers, the authors argued. In addition, chemical pesticides are much more harmful to farmers' health and the environment, and require a significant amount of technical knowledge to be used properly, they said.

"Many of the rural poor in developing countries are undereducated," said Qaim. "If they had effective pesticides, they would still have to know that the proper time to spray would be when the bollworms are in a certain larval stage, a window of opportunity that lasts a mere two to three days."