Just been emailed the proofs of a paper I wrote a month or so back, reviewing knowledge of the various mistletoe insects we have in Britain. There are, currently, six. All considered rare, but all ‘under-recorded’ as we ecologists put it because so few entomologists pay any attention to mistletoe (it’s difficult to record the specialist insects of a plant that grows at the tops of trees).
So they might not be rare at all. And 2 of them were only discovered, in Britain, in the last 10 years. Which means either a) they are new colonists to the UK or b) they simply hadn’t been noticed before.
One of the new boys is the Mistletoe Weevil – a cute little beetle called Ixapion variegatum. Labelled, by the media, the Kiss-Me-Slow beetle, when it was first found, by National Trust Ecologists in 2000, this little (3mm max) beastie is becoming a little controversial. The accepted wisdom is that it is ‘associated’ with stressed (i.e. not looking very well) mistletoe. This is because it is usually only found on stressed mistletoe. The assumption is that it prefers stressed mistletoe to live – and this is used as an argument to conserve old trees overgrown with mistletoe – as these will inevitably have stressed mistletoe and so should attract the weevil.
But is this true? Which came first? The stressed mistletoe or the weevil? The weevil’s life cycle involves egg-laying into mistletoe stems, just below the terminal bud of each shoot, with larval weevils living, and feeding, inside that shoot until they become adults. At this stage they eat their way out of the stem to meet’n’greet other adults, mate, and start over.
This summer I monitored several populations of these weevils, and realised that their larval feeding within the terminal shoot, and their eventual exit as adults, was causing enough damage for those shoots to die (see pics left – click to enlarge).
So the weevil causes the shoot to die – which could mean that instead of the weevil searching out stressed mistletoe because it prefers it, it could be that the weevil seeks out unstressed mistletoe, lays a load of eggs, which create stressed mistletoe through dieback, just as the adults emerge.
And so yes, you’ll find adult weevils on stressed mistletoe – but that’s because they created it, not because they prefer it. If this is true, then the argument to conserve overgrown mistletoe-laden trees to help the weevil might be exactly the wrong thing to do.
The weevil truth is out there somewhere…
But we need more data….
Remember to do the mistletoe survey! www.british.mistletoe.org.uk
And why not buy the book? www.buy.mistletoe.org.uk
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