Page last updated at 00:25 GMT, Tuesday, 9 March 2010

Insect that fights Japanese knotweed to be released

By Rebecca Morelle
Science reporter, BBC News


Dr Dick Shaw explains how a tiny plant-eating predator can fight the superweed spread

A tiny Japanese insect that could help the fight against an aggressive superweed has been given the go-ahead for a trial release in England.

Since Japanese knotweed was introduced to the UK it has rapidly spread, and the plant currently costs over £150m a year to control and clear.

But scientists say a natural predator in the weed's native home of Japan could also help to control it here.

The insect will initially be released in a handful of sites this spring.

This is the first time that biocontrol - the use of a "natural predator" to control a pest - has been used in the EU to fight a weed.

Wildlife Minister Huw Irranca-Davies said: "These tiny insects, which naturally prey on Japanese Knotweed, will help free local authorities and industry from the huge cost of treating and killing this devastating plant."

Alien invaders

Japanese knotweed was introduced to the UK by the Victorians as an ornamental plant, but it soon escaped from gardens and began its rampant spread throughout the UK.

It grows incredibly quickly - more than one metre a month - and rapidly swamps any other vegetation in its path.

It is so hardy that it can burst through tarmac and concrete, causing costly damage to pavements, roads and buildings.

Japanese knotweed knocking down wall (Dick Shaw)

But removal is difficult and expensive; new estimates suggest it costs the UK economy £150m a year.

However, in Japan, the plant is common but does not rage out of control like it does in the UK, thanks to the natural predators that keep it in check.

Scientists at Cabi - a not-for-profit agricultural research organisation - used this as their starting point to track down a potential knotweed solution.

They looked at the superweed's natural predators - nearly 200 species of plant-eating insects and about 40 species of fungi - with the aim of finding one with an appetite for Japanese knotweed and little else.

After testing their candidates on 90 different UK plant species, including plants closely related to Japanese knotweed such as bindweeds and important crops and ornamental species, they discovered a psyllid called Aphalara itadori was the best control agent.

The little insect feeds on the sap of the superweed, stunting its growth.

Dr Dick Shaw, the lead researcher on the project from Cabi, told BBC News: "Safety is our top priority. We are lucky that we do have an extremely specific agent - it just eats invasive knotweeds."


This timelapse footage shows Japanese knotweed growing more than 1m-tall (3ft) in just three weeks

Following peer review by the Advisory Committee on Releases to the Environment and a public consultation, the UK government has now given the go-ahead for release of Aphalara itadori, under licence, in England.

The Welsh Assembly is expected to announce its decision on the psyllid soon.

The insects will initially be released on a handful of sites.


These will be isolated and, in addition to as having the superweed present, will also have UK species that are closely related to Japanese knotweed planted there to check that the psyllid only targets the invasive species.

Dr Shaw said: "In the early stages, a contingency plan is in place so that should, in the unlikely event, any unintended consequences be detected, we will be able to do something about it.

"Insecticide and herbicide treatment will be on standby for rapid response."

If this phase is successful, the insect will be released at further sites, where it will undergo an intensive monitoring programme over the next five years.

Dr Shaw said: "On the localised sites, I would expect to see damaged knotweed this season.

"However, biocontrol is a long-term strategy - it could take five to 10 years to have a real impact."

The government believes that if the plan is successful it will reduce the costs to the building and engineering industries of clearing the plant.

However, some critics say that it is impossible to be certain that the Japanese insect will only target the superweed and could attack other species once in the wild.

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