Biological warfare is to be declared on an alien invader, Japanese knotweed, that swamps gardens and rivers, with the release of an insect to eat the virulent weed.
The decision by the Department for Environment, Food and Rural Affairs is the first allowing one non-native species, a flying insect resembling a miniature moth, to control the seemingly unstoppable spread of an alien plant.
However, it is likely to cause concern among wildlife lovers because of a long history of human interventions in the natural world ending in failure, and sometimes causing worse problems than the original, as with the cane toad in Australia.
In a public consultation by Defra last year about 20 responses opposed the scheme, though 42 were in favour.
The wildlife minister, Huw Irranca-Davies, said the fast-growing Japanese knotweed was estimated to cost £150m a year to control, and was able to grow through buildings and roads.
Fallopia japonica has also been blamed for flooding, by causing erosion to river banks and clogging up streams with dead plants.
"This project is not only ground-breaking, it offers real hope that we can redress the balance," said Irranca-Davies.
Experts estimated in 2003 that it would cost £1.5bn to fund a physical clearance campaign for Japanese knotweed.
Laboratory tests were started on pests from Japan which control the knotweed by feeding on sap from its stems, causing the plant to die back.
The tests showed the chosen Aphalara itadori did not eat any other species, including closely related British plants and important crops.
The psyllids – or plant-jumping lice, which grows to only 2-2.5mm – will be released at two sites initially, under close supervision.
If these outdoor trials are a success the trials will be extended to another six sites, none of which Defra will disclose.
The concept is similar to biological pest control practised by some farmers, using predator insects to control crop pests. The non-native predatory beetle Rhizophagus grandis was also released in Britain under licence in the mid-1980s to tackle the invasive alien spruce bark beetle (Dendroctonus micans).
On conservation and wildlife internet forums, opponents of the idea said they feared the impact on other native wildlife, for example species that might start feeding on the psyllids. One blogger compared the risk to the traditional nursery rhyme "I know an old lady who swallowed a fly" in reference to the long pursuit of one animal to destroy another – ending in the lady swallowing a horse: "She's dead of course." The Global Invasive Species Programme said that despite a few well-known failures, a third of biological control programmes to tackle pests and weeds were judged successes, and the system was often considered more "permanent, efficient, environmentally sustainable and relatively cheap" than using chemicals or mechanical removal.
"While there are some risks, which still may be considered by some to be unacceptable, biological control is increasingly viewed as being the preferred management strategy for invasive species, wherever possible, and in the case of biological weed control specifically, it has an enviable safety record," said Sarah Simons, Gisp's executive director.
Japanese knotweed, which is native to Japan, Taiwan and China, was introduced by botanists into Britain in the 19th century as an ornamental plant. It grows at up to a metre a month, and a fragment of just 0.8 grams can grow into a new plant. Invasive predators have become a global problem and are among the top causes of global species threats and extinctions according to conservation experts.
The Royal Horticultural Society suggests gardeners destroy knotweed using glyphosate-based weed-killers or by digging out the roots and cutting back regrowth, however it warns that the process can take several seasons. Experts stress that uprooted plants must be destroyed carefully to avoid spreading. "Eradication requires steely determination," says the RHS.
• This article was amended on 22 March 2010 to correct a headline that incorrectly referred to the psyllid as a moth