Searching for a bug that might not be there at all
The nature of invasive species in a changing climate dictates that managing them involves a multi-stage and often fairly lengthy process.
First up is working out whether there are possibly routes into a country. If it can’t fly, crawl or hop its way there on its own, the relentless hubbub of international trade means having a sizeable patch of water between your country and the next is unlikely to save you from possibility of arrival.
If there’s a way in, you’ve got to work out whether it could make more than sporadic and quickly-defeated appearances and actually manage to breed under local conditions. This is where quite a percentage of potential invasive species fall down, but if it can, then it’s all about cutting its chances of getting a ride into the country, and if that fails, containment.
All this means that, when done with appropriate attention and resource, there’s likely to be a period where experts are not even sure a threatening species is on their particular patch at all, but they’re still looking for it. A sensible kind of paranoia.
This is the current case with the notorious fruit pest the brown marmorated stink bug (Halyomorpha halys), or BMSB to its friends and enemies. Originally from Asia, it’s found globalisation to its liking, hitchhiking its way to Europe by 2004. Since then it’s been a tale of smelly insects, ancient warriors and scrambling in the name of damage limitation.
A stink bug hunt is very much on in the UK, led by the clever people at NIAB EMR. Adults have been spotted in the south of England, but there have been no juveniles seen to date, suggesting that it hasn’t managed to establish. This might not be that much of a surprise, as climate modelling has suggested there are only a few pockets in the south and east of England where they could potentially thrive.
Phew. But lack of evidence to suggest establishment is not to say it hasn’t. Known unknowns and all that, coupled with a deep sense that even if it’s not knocking about right now, it will be eventually.
So, the search continues, and the stakes are high — especially as those parts of England suited to establishment are also where lots of fruit is grown. The foul smell emitted by H. halys is the least of possible worries for growers, with damage to some types of pears in Italy reaching 50%, and the worst production losses in kiwi fruit orchards reported at 30%. No wonder there’s some financial backing around this one.
Backing has also been manifested in support to overcome a more complicated part of the search for this potential invader. In short, BMSB looks quite a bit like UK native species of shield bug. They’re especially hard to tell apart from others when they’re nymphs, and virtually impossible as eggs. So NIAB EMR are also working on a system to bulk analyse the DNA from samples to determine whether they really are BMSB or, indeed, not.
But once you’ve identified the interloper, what exactly can you do about it? There has been concerted research into suitable natural enemies that could be reared and released in numbers to lay the smack down on BMSB if and when they appear. As a result, enter the samurai. Wasp.
That’s right, the invasive bug itself is not the only one with an excellent name — its main identified natural enemy has an even better one. The samurai wasp (Trissolcus japonicus) is absolutely tiny but seemingly very potent parasitoid, seeking out and laying its own eggs inside those of BMSB.
The problem to date has been that, as its name suggests, it’s an Asian wasp. Introducing one non-native species to tackle another is a form of biological control which makes the authorities edgy, fearing catastrophic knock-on effects on local ecosystems along the lines of the cane toad in Australia, or, far closer to home, the harlequin ladybird in northern Europe.
In the case of a parasitoid wasp, it has to be clear-beyond-clear that it’s highly specific in its tastes i.e. isn’t about to go about ransacking the developing generations of native stink bugs that aren’t brown and marmorated. The Italian environment ministry seem convinced, with the green light set to be given to begin the release of T. japonicus in affected areas. This will hopefully prove a move that will increase confidence in biological control more generally.
For the record, I’m currently helping NIAB EMR in their latest round of BMSB monitoring work. So far, none trapped — but it has only been a month.
