Alien invaders hit the UK

[Pyan]

More research is required, on a larger scale, over a longer period of time (five years is not very long in the lifetime of a species).

Agreed - but equally, it's far too short a time for a species-dependent predator to change from knotweed to another plant - especially as the whole point is that knotweed is so different from our native plants that none of our native plant-eaters have started eating it even after nearly 170 years.