Obviously, herbicide resistance is something that is useful only when there are herbicides around to resist. Otherwise, it is just a cost that has to be borne. Insect resistance, however, might be expected to be as much of an advantage in the rough and tumble of the wild as in the cosseted environment of the farmer s field. Not necessarily, says Dr Crawley. Previous studies of wild-plant ecology have shown that the main threat to a plant s existence comes not from insect predators but from competition with other plants.
Herbivorous insects are, of course, a big problem for crops.
Indeed, they can reach plague proportions, as in the case of locusts. But that only happens because the crops in question, being laid out in fields like a banquet, form an abundant source of food. In the wild, where individuals of a species are dotted around and have to be sought out by their predators, having a few leaves nibbled away is a minor nuisance compared with having your root system strangled and poisoned by your neighbours. Needless to say, Dr Crawley s result does not imply that genetic modification of crops is environmentally safe in all circumstances. The varieties he was planting were the first, tentative products of commercial genetic engineering.