http://www.beedata.com/apis-uk/newsletters09/apis-uk0809.pdf

This article is of particular interest:

THE POLLINATION FIGHT BACK

In some recent research that will be of interest to all beekeepers, ETH
Zurich* scientists
tested whether the pollen of certain flowers contains toxins that give bees
an upset
stomach and protect the plants from the diligent pollen gatherers.
Bees and flowers are of
course a harmonious
interdependency, mostly with
equal benefits for both. The
insects obtain nectar and
pollen, pollinate the flower
and ensure the plant’s
propagation. A win- win
situation for all concerned
including other animals and
humans who eat the
fruit/crops. Scientists in ETH
Zurich’s applied entomology
group, however, now see this
relationship somewhat more soberly. Bees – besides the honey bee there are
over 600
species of wild bees in Switzerland – are herbivores that have specialized
in high-protein
pollen as their staple diet in the course of evolution. Bees need an
enormous amount of
pollen – often the entire pollen content of several hundred flowers just to
produce one
single offspring. And that can be a considerable disadvantage for plants,
stress the
researchers. Every grain of pollen that disappears in a bee’s brood cell is
really one
potential seed less. The more the bees gather pollen randomly from many
different plant
species and families, the greater the danger that it will not reach its
destination – the
stigma of the right type of flower – and fertilize it. Moreover, pollen
production also uses
up a lot of the plants’ energy. It is therefore in the plants’ interest to
reduce the number
of pollen eaters in order to prevent too much pollen being taken. Flowering
plants have
therefore developed special forms of flower in the course of time to make
gathering
pollen more difficult for bees – such as the keel flowers of the pea.
However, certain
kinds of bees have in turn adapted their bodies especially to suit such
flower shapes.

Poison keeps bees at bay
Andreas Müller’s team of researchers has now discovered a new mechanism that
plants
use to ward off pollen eaters. To their surprise, they found that a number
of bees
belonging to the genus Colletes specialize in the aster family; generalists
within the same
genus that gather pollen randomly, however, steer clear of this plant family
although it is
rich in species. Furthermore, the aster family – unlike members of the
Fabaceae family
such as peas – makes it easy for the guests to gather the pollen.
The notion of defending pollen chemically therefore seemed the obvious
explanation.
“Plants often stop themselves from being eaten by insects by storing toxins
in leaves.
Why should pollen be any different?” ask the researchers, who described this
idea as the
“aster paradox” in a recent scientific publication.
The insect researchers at ETH Zurich began a series of experiments to test
their theory.
For example, for his ETH-Zurich-medal winning doctoral thesis, Christophe
Praz fed the
larvae of specialized bees with pollen from the aster family, which was not
part of their
normal diet. Although the larvae ate the wrong food for up to 30 days, they
did not grow.
Not one species managed to develop from a larva into a bee – apart from the
specialist
bees for this plant family.
Is aster pollen inedible?
Claudio Sedivy, a PhD student in the applied entomology group, is now
collaborating
with chemist Rafal Piskorski and the student Claude Hüsser to test whether
pollen from
members of the aster family contains toxins and whether the corresponding
bees have
adapted their metabolism especially in order to use the pollen.
With their research, the ETH Zurich scientists are entering unknown
territory. The
evolutionary research appears to have ignored this aspect of floral biology,
as the
research team points out: “The chemical protection of pollen must have had
an enormous
impact on the evolution of the relationships between insects and flowers
-- 
Juanse Barros J.
APIZUR S.A.
Carrera 695
Gorbea - CHILE
+56-45-271693
08-3613310
http://apiaraucania.blogspot.com/
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