Genetically modified pest-resistant crops may not be the panacea they are made out to be, a new study shows, with specific reference to Bt cotton. The field trial by scientists in Nagpur shows that the soil the plants are grown in matters almost as much as insect-killing genes and pesticide sprays. The finding could significantly increase the amount of money farmers spend in buying and spraying pesticides. It could also mean lower yields than those promised by manufacturers of GM seeds.