Natural pesticides: a cautionary tale

Pesticides have their dangers but so too do natural biocontrol agents if they are used without care. Bacillus thuringiensis is a soil bacterium with enormous potential to control insect pests in a large variety of crops. With the toxins they produce, different strains of the bacterium kill different insects whilst leaving other organisms unharmed. The bacterium is already available in spray form and is used extensively by organic farmers. However, its misuse could also have far reaching consequences. Scientists have discovered that resistance to the bacterial toxins could evolve in insect pests and spread much more quickly than was previously thought. A study conducted on the diamondback moth, Plutilla xylostella, a major pest of cabbages and other leafy crops at the University of Arizona in the US, has produced some thought provoking revelations. It was initially discovered that a single gene, rather than multiple genes, would confer resistance to all four toxins to which the moth had previously been susceptible, despite the fact that the moths had been exposed to only a single toxin. The researchers also detected that in laboratory populations of moths exposed to bacterial toxins resistant individuals appeared in consecutive generations in far greater numbers than had been estimated. The fast developing resistance shown by this one insect pest should caution biotechnology companies wishing to isolate these toxin-producing bacterial genes and introduce them into crop plants. The toxin genes, which would give plants a natural immunity to insect pests, are already being trialled in a range of crops including cotton, maize, tobacco and soya bean. Hopes of reducing pesticide use, protecting the environment and increasing crop yields could all be realized should the genetically modified crops prove to be a success; but there are now fears that extensive use of the technique could lead to a wide variety of engineered crops being produced and grown, which in turn may lead to a rapid increase resistant pest populations. New Scientist 8th March 1997 IPC Magazines Ltd King s Reach Tower Stamford Street London SE1 9LS UKPesticides have their dangers but so too do natural biocontrol agents if they are used without care. Bacillus thuringiensis is a soil bacterium with enormous potential to control insect pests in a large variety of crops. With the toxins they..