Science Questions

How do some orchids mimic insects?

Sun, 11th Apr 2010

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Question

Chris Lait asked:

Hello,

 

Could you please tell me how some orchids can replicate a femael bee, scent and visually to attract a male bee?  Does this mean plants can see?

 

Many thanks

 

Chris Lait

 

ps I've downloaded a 100 plus of your podcasts and enjoy listening to them when i'm driving my lorry through the night.

 

Answer

There was a wonderful paper written by a lady called Jennifer Brodmann, who is a researcher at the University of Ulm, and she was on the Chinese island of Hainan looking at an orchid called Dendrobium sinense.  Now, this is a really interesting orchid because no one knew what pollinated it.  It makes these beautiful flowers.  It's a white flower with a red centre, but it's rewardless.  In other words, the flower doesn't give anybody anything if they come and visit it.  So she decided to do a stakeout and she watched this flower , 121 hours of footage to see what came by.  And 35 insects paid a visit of which the majority - over 30 - were a kind of hornet.  And she thought, "That's interesting."  At closer inspection, revealed that these hornets didn't come in and spend much time loitering there.  They flew in and pounced on the flower and then abruptly left.  But when they looked more closely, they saw that as the hornet was doing the pouncing, it was actually depositing a bit of pollen on the orchid, fertilizing it and also picking up some pollen to take to another flower.  So they thought, "There must be something which is attracting this hornet to this flower."  So they made extracts of all the chemicals that come out of the flower and they found one really interesting one.  It's eicosen-1-ol.  And this particular molecule is a pheromone made by bees.  And, in fact, it's an alarm pheromone that bees make when they want to tell other bees about something exciting going on.  And what they realized is that this hornet species eats bees and it feeds the bees to its young hornet larvae.  So what the orchid is doing is making itself smell like a bee to attract a hornet, to get itself fertilised.  And it's doing it by making the same chemicals that the bees would and, thereby, fooling the hornet, so a wonderful example of sexual kind of subversion going on.

The point is that the plant has evolved to have the same genetic pathway or the same synthetic pathway that can produce these chemicals because this is the way in which it gets itself pollinated, and very effectively too by the look of it.

If you want to read it, it was actually published in Current Biology, last year, Jennifer Brodmann, a wonderful bit of science.

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Chris Lait asked the Naked Scientists: Hello,   Could you please tell me how some orchids can replicate a female bee's scent and visually to attract a male bee?  Does this mean plants can see?   Many thanks   Chris Lait   ps I've downloaded a 100 plus of your podcasts and enjoy listening to them when i'm driving my lorry through the night. What do you think? Chris Lait , Thu, 8th Apr 2010

Hi there,

No, that doesnīt mean, that plants are able to see the insects they are imitating.
And that is not necessary, because evolution is not specific. It is not, that any plant decided, which smell or appearance would do best, to reach the goal to reproduce. Itīs more that individuals of one species differ a bit.
In fact the insects formed the plants appaerance via selecting those varieties, which smells the best for example. .. and so on.

aj atrox, Mon, 12th Apr 2010

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