Monday, June 7, 2010

Weevil Intent....


I felt a deep sense of unease when I found this weevil crossing our garden path today, because it's a near certainty that its larvae, which feed underground on the roots of plants, are already doing serious damage to some of our plants. The worst culprits are vine weevils Otiorhynchus spp.- and I'm pretty sure that's what this is. The adults nibble conspicuous holes in the edges of leaves, using jaws on the end of that elongated snout, but the first sign that their larvae are at work is when a plant suddenly wilts - because its root system has been destroyed.


Vine weevils can be particular problem if you grow cyclamen or primula speicies, and since I have a collection of Primula auricula varieties growing in pots in the garden, maybe it's time to check their root systems for the fat white grubs of this destructive beetle.

Vine weevils belong to a tribe of beetles called the Otiorhynchini, notable for having no wings and for being able to breed without the need for males, reproducing clonally via parthenogenesis. This goes some way to explaining why they are so prolific - if males are needed, only the female half of the population can lay eggs but if a species is parthenogenetic every individual does so..... and vine weevils can lay up to 800 eggs. There are many closely-related species and you can find a fine illustration of some of them here.

17 comments:

  1. Super macro pictures of this little monster, Phil. I hope it doesn't do too much damage to your garden.

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  2. It's amazing how many insects are parthenogenic! What I once thought was highly unusual is turning out to be pretty darn common.

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  3. Cracking shots of every gardeners nightmare Phil.
    They certainly are destructive little blighters.

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  4. Thank you for sharing your superb macro shots with us, Phil - and for the warning!!

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  5. Great macro shots of the destructive little pest Phil. I lost all my strawberry plants to vine weevil grub activity last year.

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  6. They are the bane of my fuchsias' lives-can't tell you how many I have bought over the years.Great macro photograph.

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  7. Hi Emma, it's a while since I've had a problem with these, so I'm keeping my fingers crossed that this wasn't the first of many..

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  8. Hi Ellen, yes - even komodo dragons, apparently. I think the smartest ones are those that switch between normal sexual reproduction and parthenogenesis, like aphids do - exploiting the advantages of both.. best wishes,

    Phil

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  9. Hi Keith, I'll be might relieved if this turns out to be the only one, but somehow I don't think it will be..

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  10. Hi Richard, my kind of macro subject - they move slowly and can't fly away! best wsihes,

    Phil

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  11. Hi John, thanks for reminding me about the strawberries - I'll check the roots of those too - I'm growing them in pots in the greenhouse this year (and picking a good crop right now)

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  12. ... and thanks for reminding me about the fuchsias too threadspider - good grief, is there anything they don't attack?!!

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  13. Sorry Phil I quite like the look of it. Mind I don't have a garden. Come to look again your garden path looks better than my carpets.

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  14. Phil, are you sure this is the destructive, parthenogenetic species? I got an invasion a few years back and mine were quite different, with the thorax quite bare and with granulations (I would say they were Otiorhynchus sulcatus from the plate you pointed at. Yours looks very hairy, and actually, quite handsome! In any case, after several of my succulents dropped literally out of the pots when their roots were completely eaten out - fortunately we could easily get cuttings from all of them - we used the comercially available biological control, parasitic nematodes (we got from greengardener). After a couple of applications with the nematodes dispersed in water I haven't suffered from them. I have seen one or two in the garden, but I think the main problem is in pots, where there is no natural predators for the grubs.

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  15. Phil, I think your weevil could be Liophloeus tessulatus
    check it on this page, where it says how to distinguish it from the Otiorhynchus lot. Still parthenogenetic and still eats plants, but it would not be much of a pest.
    http://www.bugsandweeds.co.uk/weevils.html

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  16. Hi Adrian, it does look quite amiable..

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  17. Hi Blackbird, thanks! That's definitely it. I was hoping someone might be able to ID it for me ... you may have noticed I was circumspect about giving it a name as I wasn't certain what it was, and there are quite a few species to choose from. One of the confusing features is the way in which those 'hairs' seem to have worn away from parts of the exoskelton - e.g. on parts of the elytra in the top image, revealing an underlying pattern of pits. I have to admit that I also sharpened the image a little in Photoshop and when you do that it always exaggerates the appearance of any fine hairs. I recall reading about the nematodes but have never tried them, but will if my auriculas come under attack. That's an extremely useful web site - much obliged! all the best, Phil

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