ALTHOUGH the introduction of insect-resistant transgenic crops is not imminent in the UK, scientists at IACR-Rothamsted have been developing protocols for assessing their possible side effects for more than two years, with the help of DETR funding.
"Our goal is to develop methods which will enable us to look at and quantify any risks across a range of crops," explains Dr Guy Poppy, an entomologist at Rothamsted. "Growers need to know that if and when insect-resistant crops are available, they will be safe to grow."
Dr Poppy adds that transgenic insect resistance is years behind herbicide tolerance, and that most of the current commercial crops are not very relevant to the UK. "Maize is the first crop which is likely to be commercialised in Europe, but UK growers dont have a major problem with the European corn borer, so its not really applicable here.
"But in the USA, they are already growing cotton, potato, maize and tomato which has had insect resistance engineered."
Together with his colleague, Dr Tanja Schuler, Dr Poppy has been studying the likelihood of tansgenic plants disrupting natural biological control in the field.
"Remember that crops support both pest insects and the predators that feed on them, playing an important role in the regulation of their populations. The most obvious way that transgenic crops can affect natural enemies is by severely depleting the supply of some hosts.
"But its also important to bear in mind that any method of protecting crops from pests, whether it is chemical or biological, entails some disruption of insect numbers," he continues. "Its not unique to transgenic plants. So the impact of biotechnology must be judged alongside the impact of conventional control methods."
He believes that a major benefit of insect-resistant crops will be a reduction in reliance on insecticides. "That, in turn, will help maintain beneficial populations."
To date, the work has not uncovered any unexpected effects. "We start in the laboratory and try to create a worst case scenario. Any subtle changes in insect behaviour can then be noted, and a decision made as to whether to proceed through the testing scheme."
The next stage is to scale up the study and look at the effects on both the target and the non-target population over time. "Field studies are the last stage, but we have a good idea of what we may find before then."
Dr Tanja Schuler points out that all of the insect-resistant transgenic plants commercialised to date express toxin genes derived from the bacterium Bacillus thuringiensis (Bt). "But there are also two groups of plant-derived genes used to confer insect resistance – inhibitors of digestive enzymes and lectins. So far these do not give such high levels of insect control."
She says that the number of predators may decline owing to host depletion on a transgenic crop. But she also points out that their persistence is not necessarily threatened if other nearby crops support host or prey species.
"Field experiments with Bt cotton and Bt maize have shown little reduction in beneficial insect populations as a whole," she adds. "However, large-scale commercial planting of highly resistant plants is likely to have repercussions for species specific to target pests." *