But neither the Government nor the private sector has come up with the research funds he needs to demonstrate that the South African caterpillars are up to the job.
Bracken is known to cause cancers in cattle and sheep and is suspected of causing it in humans. It also harbours a sheep tick which can give humans a chronic illness called Lyme disease.
It is a fairly primitive but highly successful plant - the same species is found on every continent apart from Antarctica. In Britain, bracken has invaded uplands and lowland heath, covering the countryside in a dense, monotonous carpet. It discourages most wildlife and renders the land useless for grazing.
Bracken in England and Wales now covers an area the size of Lancashire. It has increased because fewer cattle are kept on the uplands - they trample and kill the young shoots - and because farmers work hillsides less intensively now. There is no longer enough money or manpower in upland farming to control bracken by cutting and burning.
Until recently, the only alternative to traditional farming practices was to use a particular weedkiller. Since not all bracken-covered land is accessible from the ground, this usually has to be sprayed from a helicopter. Spraying is expensive and any patches that are missed soon start to spread across cleared areas.
The caterpillars carrying the hopes of Professor Lawton are Conservula cinisigna and Panotima. In their native South Africa, bracken is their sole diet. The professor, who heads the interdisciplinary Centre for Population Biology at Silwood Park, Ascot, Berkshire, has been investigating them for a decade. His hope is that they would thrive here. Britain has a similar climate to the Eastern Cape mountains where they live and none of the predatory insects and animals that are the caterpillars' enemies.
The caterpillars must be screened before they are released into the wild to make sure they do not harm other British plant species or crops. So far they have been tested in the laboratories at Ascot. Professor Lawton has now obtained government permission to test the caterpillars outside the laboratory. This stage took many months, partly because the application is scrutinised by a government-appointed committee of experts on introducing exotic species. He also had to get permission from the Ministry of Agriculture to import the caterpillars.
The next and final stage before putting the insects to work in the wild is to leave them on bracken in large outdoor cages, double- meshed to prevent escapes, for three years. The caterpillars would metamorphose into moths, which would lay eggs, ready to attack the next spring's growth. This outdoor trial would show how effective the caterpillars are at devouring bracken and how they adapted to the climate.
It would cost pounds 200,000, spread over three years, but Professor Lawton can find no single body to put up the money. His research has already cost about pounds 150,000 and most of that has come from government. 'It's fairly ironic that having almost got to the stage where we can apply the knowledge we've gained we run into trouble,' he said. 'It's symptomatic of the way research is treated in Britain. There's money for pure research, but when it comes to applying it for a useful purpose it dries up.'
The Ministry of Agriculture has turned him down, although it has said that it might provide part of the money. Professor Lawton is now trying to set up a funding consortium involving the ministry and other, mainly government, bodies. Jim Taylor, Emeritus Professor at the University College of Wales in Aberystwyth and a leading bracken expert, said: 'I think we have to go for the kind of biological control of bracken that Professor Lawton is studying, but it can never be the complete answer. Bracken follows whenever man clears the land for agriculture and I think we'll never win.'
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