Invasive Pests And The Japanese Knotweed Consultation

There's an episode of "The Simpsons", where invasive lizards are found to be an effective predator of pigeons in Springfield (Season 10, episode 3, "Bart The Mother"). About 21 minutes in, Principal Skinner and Lisa have the following conversation:

Skinner: Well, I was wrong. The lizards are a godsend.
Lisa: But isn't that a bit short-sighted? What happens when we're overrun by lizards?
Skinner: No problem. We simply release wave after wave of Chinese needle snakes. They'll wipe out the lizards.
Lisa: But aren't the snakes even worse?
Skinner: Yes, but we're prepared for that. We've lined up a fabulous type of gorilla that thrives on snake meat.
Lisa: But then we're stuck with gorillas!
Skinner: No, that's the beautiful part. When wintertime rolls around, the gorillas simply freeze to death.

This came to mind when Hubster and I were talking about the news that Defra are opening a consultation on the introduction of a tiny louse, Aphalara itadori, to control the invasive weed Japanese knotweed, Fallopia japonica. It's an elegant idea - forget glyphosate, napalm, flame-throwers, hot tar, all those normal gardening methods - why not use Nature Itself? Biological control is nothing new. Attract frogs and toads to your garden to get rid of slugs; better still, apply a rinse of Nemaslug - parasitic nematodes that infest the bodies of slugs. Do the same for vine weevil and leatherjacket larvae. Get predatory mites that feast on RSM into your greenhouse.

According to Defra:

The psyllid has been tested on 87 non-target types of plant including those closely related to Japanese knotweed as well as ornamental plants and important crops, to determine whether it will feed on other plants. The findings suggest that only a few closely-related non-native knotweeds are potential hosts in Britain.

Okay, they've got some good evidence there (although if I grew rare ornamental knotweeds in my exotic garden I wouldn't be too thrilled at the prospect of another pest to deal with!). It may all be fine, and if successful it will be less damaging (and less of a public health issue) than using weedkillers. And let me clarify - Japanese knotweed is a horrible invasive plant, and I can honestly say I would be delighted if it could be eradicated from the UK.

But I have my concerns. The Pest Risk Assessment is a good read. Here are a few things that leapt out at me:

Page 3: The psyllid overwinters on the bark of conifers in Japan; this is thought to be for shelter only with no significant damage inflicted as a result. It is not known how it would overwinter in the PRA area but it is likely to be on conifereous trees and no feeding damage is envisaged.

It is not known?! As a grower of many, many conifers, I'm not entirely convinced that's a good enough answer for me.

Page 3: The winters in the psyllid's native range in Japan are harsher than the UK with much more snowfall. The summers can be very hot and dry. So, in general, climatic extremes are greater in its native range in Japan, compared to GB.

So it looks like our psyllids won't be making like the Springfield gorillas and freezing to death. Have the effects of a milder winter been fully investigated?

Page 6: Threats to non-target species that were unable to support development to adult are presumed to be low, but if the knotweed host is severely damaged or eradicated there is a risk of some "spillover" damage in the short term.

So if the louse succeeds in its task, it might start on some of the other local species. What I couldn't find on my scan of the documents was anything to say whether the louse would have predators. Will insectivorous birds like blue tits happily predate on the psyllids, or will knotweed availability be the only limiting factor?

It's food for thought. I'm certainly not a target consultee (I don't even have a problem with it in the garden), but if any of you would like some input, the full consultation is available on Defra's website.