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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 more than £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.

Dr Dick Shaw from Cabi, a not-for-profit agricultural research organisation, explains how the bug - called a psyllid - attacks knotweed.