Monday, May 16, 2011

Rhubarb Weevil


Rhubarb Weevils (Lixus concavus) are found throughout most of the United States, and as their name indicates are fond of rhubarb as well as dock, sunflower and thistle. The one pictured here is feeding on curly dock that grows near our garden. I noticed several of them on the leaves beginning in mid-April. I've not discovered any severe damage being done to the dock, and I would assume it would take a huge infestation of these beetles before any real harm would come to the plants. Since dock is not a plant I am particularly fond of I leave them be. I do not grow Rhubarb, so no worries there either. For gardeners who do grow and value their rhubarb, then control may need to be implemented. From everything I've read, the best way to control them is to simply pick them off the leaves of the plant. They are large enough at a 1/2 inch in length to see which makes finding them and removing them by hand is no real problem. It is much better than using pesticides, which can be harmful to beneficial insects. The female will lay her eggs inside the stems of plants. The eggs hatch and feed from within the plant. They are unable to survive inside the stems of the Rhubarb plant because of its growth habits. The plant continues to grow and constricts the eggs or larvae and they will not reach maturity. Good news there! However, they will survive inside the wild host plants like thistle, dock and sunflowers. So if you want to help control their numbers remove the wild host plants sometime in July and this will prevent them from completing their lifecycle. Those beetles that are left alone will overwinter in leaf-litter and become active again the following April or May.



 These weevils (A.K.A. snout beetles) are actually black,but are covered in a yellowish-orange powdery substance that gives them a completely different appearance. I've never actually seen a black one, each one I find is always covered in this orangish powder. 


When these beetles sense danger or are disturbed they will "play-dead" and roll over on their backs, legs curled and lay completely still (pictured below). Sometimes they will roll completely off the leaf and disappear in the leaf litter on the ground. 




Weevils are one of my favorite beetles and are the largest groups in the order coleoptera with over 60,000 species worldwide. These beetles look like little elephants carrying their trunk around on their face. This trunk-like snout is the mouthpart of the weevil and contains chewing mandibles at the end of the snout which allows them to chew on the preferred food plants.  Many weevils are damaging to crops and billions of dollars are spent each year to control them. Fortunately the weevils that live on our farm pose no real threat to anything and are able to go about their business undisturbed.

11 comments:

  1. They are not the prettiest creatures I have ever seen.

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  2. Interesting that people call them after a plant that is no real host to them. We have some in the same genus here in AZ that are in all kinds of Asteraceae, mainly Seep Willow (Baccharis salicifolia) They are mating and boring their holes for eggs right now.

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  3. That's got to be one of the cutest bugs I've ever seen, almost as good as those water bears they've just taken into space!

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  4. I like to look these over also. It looks like me after working in the lilies, the pollen really sticks to you.Thanks for the ID, it was a beautiful area with all the hyacinth and larkspur in bloom.

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  5. wow, that first shot is SO GREAT! I love their little tube-y noses. SO cute. =)

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  6. @Emma, it is funny you say that, I think weevils are adorable. That little trunk they carry around in the form of a mouth is hilarious.

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  7. @Margarethe, I agree it is odd that they would be named after plant that they feed on but can't use as a host. Perhaps when they were named they were spotted on Rhubarb and believed to be using it as a host. Once it was discovered that they did not, they name had already stuck.

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  8. @ Queen of Strings....I know right? I love weevils.

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  9. I love curly dock for finding insects, it seems there is always something on it feeding. You are welcome for the ID on your flower, but the real thanks goes to James Trager....I sent him your image and he was able to identify it for you. :o)

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  10. Thanks Bio, I am always amazed when I manage a decent shot! LOL I think weevils are adorable too. THose noses are comical.

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  11. Aww, its cute! Never seen a bug like that here in the Philippines! Rhubarb Weevil at least I learned something new..

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