Although the scientists believe they have addressed many of the fears over the safety of the new pesticide, the research is bound to raise questions about whether such genetically altered viruses should be released into the environment.
The issue was highlighted by last week's disclosure in the Independent that government safety inspectors stopped research at Birmingham University on a virus genetically engineered to carry a cancer gene. They were concerned that it could infect workers in the laboratory, or put the public at risk if it escaped.
The researchers who conducted the pesticide field trial, however, have followed all the Government's safety procedures to the letter and said they had taken all necessary steps to ensure that the genetically altered virus did not threaten humans or the environment.
The field trial was conducted last year near Oxford, but the results have only recently been prepared for publication. They show that the genetically engineered virus with the North African scorpion toxin is 'significantly faster' at killing caterpillars than its natural forms.
Professor David Bishop, of the Natural Environment Research Council's Institute of Virology and Environmental Microbiology at Oxford, who led the research project, said the ground was prepared for further improvements to the pesticide. 'This is the first field trial in the world of a genetically improved insecticide. It's a first step along the road to producing something that can compete with chemicals.'
He emphasised that the toxin was highly specific to certain insects and harmless to humans and other mammals. The virus, of a type known as a baculovirus, normally infects caterpillars of the alfalfa looper moth and further research will investigate whether the genetic alterations affect the range of species it acts on.
Professor Bishop discounted suggestions that such work could produce a deadly mutant virus that runs out of control: 'The idea that you're going to introduce mutations or genes and turn the virus into some sort of a triffid is unreal.'
He said that the introduction of the scorpion toxin to speed up the action of the virus was necessary in order for such 'biological pesticides' to be as effective as chemical sprays. The toxin paralyses and kills the caterpillar within a few days.
Professor Bishop's research has been approved by the Health and Safety Executive, the Department of the Environment and the Ministry of Agriculture, Fisheries and Food. 'We're going slowly and steadily,' he said. 'The work has been going on for nine years.'
In 1989, the Royal Commission on Environmental Pollution said that Professor Bishop's 'step-by-step' approach reduced risks. But environmental groups maintain it is not always possible to assess all the risks posed by genetically engineered organisms released into the environment.