On 2009-07-13 10:40:53 +0100, Davy said:

My crop of mangetout is well down on last year and my runner beans are
not setting at all.

Earlier in the year we had more honey bees than for years; but none now.
Instead we have lots of bumble bees, as many as a dozen on a single
flowering plant - but none on the runner beans. The RHS state that
bumble bees cannot polinate runner beans.
snip
I don't pretend to have the answer but this site doesn't agree about
bumble bees and the RHS site seems to refer to the short tongued bumble
bee not helping with pollination:

Pollination and Isolation

Runner beans are pollinated by bumblebees and honey bees and cannot
cross with other types of beans, though they will cross with other
runner beans quite readily. For this reason we recommend a minimum
isolation distance of 800m between runner bean varieties to be certain
of maintaining varietal purity.

If you know of other runner beans being grown within 800m of your plot,
or if you wish to save seed from two or more types of runner bean on
your own plot, isolate varieties either with a fleece bag around each
truss or with a large insect proof cage around several plants. It may
be easier to cage a tepee rather than a row. You then must hand
pollinate each newly opened flower with a thin paintbrush. Do this by
hand each day, simply pressing down on the lower (left) keel of each
newly opened blossom to mimic a bee landing. Then use the paintbrush to
transfer the pollen from anther to stigma. You should use pollen from
another plant of the same variety rather than from the same flower or
plant. If you are growing more than one variety, remember to wash and
dry the paintbrush between varieties.
http://www.gardenorganic.org.uk/hsl/...nner_beans.php

I wonder if, next year, you could arrange for a local bee keeper to put
a hive in your garden or on your allotment?

--
Sacha
www.hillhousenursery.com
Shrubs & perennials. Tender & exotics.
South Devon