Oh dear.
To introduce another alien species in attempt to get rid of the first is, in my opinion, likely to cause further problems on its own account in due course.
Generally speaking,
any alien species, whether introduced deliberatley or accidentally - and I do not include anything that has arrived naturally by range expansion - has caused problems sooner or later for native species and the environment/habitat. Think grey squirrels, domestic cats, rats and hedgehogs on islands where none occur naturally, mink, ring-necked parakeets, bunnies in Australia, wild boar, ex-pet ninja-turtles.... I don't know much about alien bugs and insects but I'm pretty sure some of those have caused problems too.
There must be a better way to eradicate Japanese Knotweed, surely, even if it is labour-intensive and needs to be repeated annually for a while....
