From: ted.held at us.henkel.com (ted.held at us.henkel.com) on 2007.10.23 at 16:58:25(16591)
Dear Friends of Botanical Curiosity,
There is an interesting article in the October 5, 2007 issue of Science
magazine entitled "Odor-Mediated Push-Pull Pollination in Cycads". The
reason I feel comfortable about sharing it to this list is that the
"push-pull" mechanism involves the warming of the cycad inflorescence and
the emission thereby of chemicals. Sounds like some aroids, no?
It seems they have a cycad in Australia called Macrozamia lucida and they
(especially the male) self-heat daily. This involves a temperature rise of
12 degrees C above ambient. This cycad is pollinated by a thrips (and some
of you thought thrips were solely placed on earth the vex horticulturists)
of a primitive thrips species called Cycadothrips chadwicki. During the
hours of 1100 and 1500 (11 in the morning to 3 in the afternoon) the male
plant heat up, emitting "male volatile emissions", which are attractive to
thrips in the absence of heat. Evidently, the warmed male odors are
obnoxious and/or toxic and drive the thrips, laden with pollen, out of the
male plant and toward the less-noxious female plant. The article states
that thrips that remain tend to die within ten minutes.
Once the heating cycle ends, the chemical activity and toxicity dissipates
and the odor reverts to being attractive to thrips again, whereupon the
thrips migrate back to the male cycad for another load of pollen. They
then discuss the specific chemicals and some experiments they did, which
may be less interesting to the general reader.
Finally, the article wraps up by observing "Floral scent may have
originally evolved to deter herbivores, and this system may represent a
conserved early intermediary in the evolution of seed plant pollination."
There are some interesting speculations there for the botanically- and
paleontologically-inclined.
For reasons I do not understand, the whole article can be read without
charge at the Science magazine site:
http://www.sciencemag.org/cgi/reprint/318/5847/70.pdf
They also claim to have a movie clip showing the mass exodus of thrips,
but I could not get it to download to my computer.
We tend to think of odor production in aroids as strictly attractive. But
I wonder if some repellency might also take place in order to force pollen
to another plant. Otherwise, why would a bug ever leave?
Ted.
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