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Debate over a GM rice trial in China.

IN THEIR REPORT “INSECT-RESISTANT GM rice in farmers’ fields: assessing productivity and health effects in China” (29 Apr., p. 688), J. Huang et al. found that farmers growing insect-resistant GM rice obtained higher yields with less use of insecticides than farmers growing conventional varieties. Huang et al.’s methodology does not, however, permit discrimination between two alternative hypotheses explaining the farmers’ decision to spray Bt/Ti rice less often: (i) farmers sprayed Bt/Ti rice less often because they observed fewer lepidopterans (the main insect pests that would be affected); or (ii) because the farmers knew beforehand which variety they were growing, they decided a priori to spray Bt/Ti rice less often. Were farmers responding to real effects of Bt/Ti rice, or were they acting on faith that they needed to spray conventional varieties frequently but Bt/Ti rice only occasionally? To test for real effects, a subset of farmers should not know which type of rice they are growing. This can be accomplished by conducting a double-blind study or by adding a placebo treatment. To assess farmers’ responsiveness to pest infestation, pest levels should also be analyzed. The influence of farmers’perceptions on pest management in rice is well known. Farmers tend to spray more insecticides than needed (1–4) unless their perceptions are changed. Spraying has been successfully reduced without yield loss and without adoption of Bt/Ti technology by rice farmers under a number of different circumstances (5–8). Perhaps the Chinese farmers in this study could also have reduced spraying of the conventional varieties without yield loss. In the precommercialization evaluation of the impact of insect-resistant GM food crops on productivity, health, and the environment, we stress the importance of distinguishing between perceived and real effects of the transgenic variety. K. L. HEONG,1 YOLANDA H. CHEN,1 DAVID E. JOHNSON,2 GARY C. JAHN,1 MAHABUB HOSSAIN,3 RUARAIDH SACKVILLE HAMILTON4 1Entomology and Plant Pathology Division, 2Crop, Soil, and Water Sciences Division, 3Social Sciences Division, 4Genetic Resources Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.