Fight fire with fire

Since our hunter–gatherer ancestors began to develop agriculture more than 10,000 years ago, farmers have been battling with Nature to protect their cultivated plants against pests and diseases. Organisms from all kingdoms of life—from mammals and insects to bacteria, fungi and viruses—are attracted by the easy pickings that large fields of plants represent, and farmers have sought to contain them by using various strategies, including the earliest, simplest and generally most successful one: crop rotation. Early farmers also turned to toxic elements—such as sulphur, arsenic and mercury—to fight pests and pathogens, with little awareness of the danger that these toxins presented to humans, let alone to the environ ment. The advent of organic chemistry eventually led to the development of synthetic compounds—in particular, organochlorine insecticides such as DDT—with initially spectacular successes in the fight against pests. However, over time it became clear that DDT and other organic pesticides are slow to degrade, persist in the environment and accumulate in the fatty tissues of predators, in particular mammals and birds. In 1962, the American naturalist Rachel Carson (1907–1964) published her landmark book, Silent Spring, in which she detailed the severe effects of organochlorines on humans and the environment; the book not only triggered the environmental movement but also led to subsequent bans on organochlorine pesticides. Over time, the chemical industry has developed other classes of insecticide, including organophosphates and carbonate pesticides, which degrade more quickly. Yet, these have also been restricted by many regulatory agencies because they are even more toxic to humans than are organochlorines. Inspired in part by Carson’s book, interest and investment in biological measures to control pests began during the 1960s. But, for almost two decades, the production and use of biopesticides were largely confined to a cottage industry, with low acceptance from most farmers because of poor efficacy and quality control. In 1981, however, the first applications of genetic engineering represented something of a breakthrough for biopesticides. The cloning of the delta endotoxin—an insecticidal toxin—produced by the widespread soil bacterium Bacillus thuringiensis (Bt), and its subsequent expression in and purification from Escherichia coli, allowed the large-scale production and use of this highly efficient pesticide (Schnepf & Whiteley, 1981). The ability to express the toxin in other organisms, as well as mod ifications made to the bacteria themselves, opened the door to large-scale production of various biopesticides and attracted large agrochemical companies.