Well, it seems it's actually come true. As reported on this blog and elsewhere, CABI have been looking at possible biological control agents for the invasive Japanese knotweed Fallopia japonica. They're now ready to release one, the jumping psyllid plant louse Aphalara itadori

To their credit, CABI have done a remarkably good job in getting publicity not only for the process of assessment, but also for the release. Few with even a passing interest in knotweed can be unaware of the work they have been doing, or the results. This is no mean achievement for what might otherwise appear to be a fairly non-dramatic bit of biodiversity-based science.

But needless to say this hasn't stopped the hard of thinking from gathering their meagre wits and bleating caution. Luckily the Daily Mail is there to provide an outlet for such folk.

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Check out the unedited reader comments on this Mail article which are typical of those I have seen and heard.

These things will eat all your crops then we will have to import gmo food exportedfrom india. These bugs are not here just for knotweed do not believe that.
- jan, west Sussex, 14/10/2008

This stuff is out of control because it was allowed to get out of control in the first instance, all that is wanted is a no nonsense approach, ie, get men out there with petrol trimmers and cut the plants down, keep doing it and they will be finished, like all plants they need leaves in order to grow, this is putting it in short words for the over educated to understand.
- William Owen, Cardiff Wales, 13/10/2008

did they learn nothing from Meximatosis (escuse spelling)... They bought that 'bug' from Australia to control the rabbit population and that went horrifically wrong. These 'bugs' are native to these countries for a reason. Do not mess with nature.
- rose, london UK, 14/10/2008

Of course, a no-nonsense approach. Why didn't anyone else think of that? The trouble is, these, and many other commentators just haven't been looking at the background to this proposed release. They write as though they alone are in possession of this extraordinary insight: introduced species can affect native wildlife! Well, duh, what do they think that CABI has been looking at for the last ten years? Perhaps there is a reason why this is the first such introduction authorised in the whole of Europe - maybe these CABI guys haven't just been sitting around in their white coats enjoying the warmth of the glasshouses. And perhaps their anticipation of this all-too-predictable objection is the reason they have made so much of their work available for study online, often in easily-understood non-technical terms (see the video below, for example). It's easy - sometimes too easy - to advocate the precautionary approach. That emphasis also, as ever, makes a good hook for a journalist who prefers to highlight a debate with two opposing 'sides', even when there is none. But in this case there is no such debate - or if there was, it is over. The research is done, consent is granted, the louse will be released. And this Ranger, sick of endlessly spending money on spraying knotweed, says a loud hoorah for that.

This video is by Dick Shaw, one of the lead researchers at CABI working on the knotweed control study.
TL;DR It's twenty-two minutes long but skip to 3:00 to avoid a rather over-long advert for CABI. There's some good background on biological control and then the knotweed section of the video is the middle 10:00 - 20:30 minutes.