This fine miscanthus is not pollinated by insects. Grasses are wind pollinated, as are conifers and many woody plants such as elderberry, (my own hay-fever bête noire). Wind pollinated plants have their own special strategies to ensure pollination. They produce prolific amounts of very small light pollen that is carried on the air. They frequently have separate male and female flowers, the latter with large receptive stigmas often held away from small leaves.
|Birch catkins produce copious pollen before leaves appear and get in the way|
Before you go out and dig up your grasses it is worth reflecting that pollinating insects require more from flowers than nectar. Bees have ‘pollen baskets’ to transfer protein rich pollen back to their broods and also collect waxes and other nutrients including stimulants as we will see. Bees are frequently observed visiting grasses to collect pollen. Many honeys have flavours of wind pollinated plants. A bee’s electrostatic charge can attract air born pollen which gets carried back to the hive.
|These ethereal grasses are all wind pollinated|
Most of our garden plants, are insect or animal pollinated. Apparently 200,000 different organisms provide this service worldwide. This pollination strategy usually involves attractively coloured flowers, nectar production, rich aromas and large sticky pollen. In many cases animals and plants have evolved in tandem as each make their own contribution to the efficiency of the joint venture - the transfer of pollen between plants and the provision of nutrition for the animal vector.
I use the terms ‘rich aroma’ and ‘attractive’ advisedly, the aroma may be foetid and the attraction visible to the insect and not to ourselves. Indeed some colours imparted in modern varieties by selective breeding might not be visible to the bees!
Bees are able to see ultra-violet colours invisible to ourselves.They are sensitive to colour at the blue, yellow, violet, end of the spectrum.They are not attracted to reds but other pollinators are. Bees perception of a flower is very different to our own as this link shows.
|This picture would seem to belie my assertion that bees are not attracted to red. Could other attractions have seduced her, or is she seeing something different?|
|The bee does not see the dandelion as just yellow|
Most of us are familiar with nectar guides. These are the visible, or to us, sometimes invisible guides, for insects to find their nectar. From the plant’s perspective, it ‘wants’ the insect to be covered with pollen as it seeks nectar. Most of our plants have many different potential pollinators who might benefit from this flight directional service. Others have evolved very specific mutual exclusive arrangements. The survival of the ivy bee is completely dependent on ivy, although the ivy is not uniquely dependent on to the bee. Yucca’s relationship with the yucca moth is completely exclusive. Without each other, the yucca cannot set seed and the moth cannot breed.
If bees moved between different flowers in a completely random fashion, flowers would be cluttered with different plants’ pollen. Bees often display flower constancy where an individual bee remains loyal to his particular provider.
|A basket of pollen|
There have recently been two fascinating findings about pollination by bees.
The New Scientist has recently reported research by Daniel Robert at the University of Bristol. Bees carry a positive electrical charge and flowers are negative. Bees appear to be sensitive to an electric field and it would seem that plants might have evolved to create a ‘bulls-eye’ shaped electrostatic field to guide bees to the pollen. It does appear that as a succession of bees visit a flower the plants electrostatic charge is depleted and so too the pollen. To paraphrase Daniel Robert the plant is saying to the bee, “ ignore my ‘come on’ signals, my electrics aren’t right, come back later!”
Caffeine might give bees a buzz. Thanks to National Geographic for this newly reported research by Geraldine Wright at Newcastle University and thanks for the pun! Research on the coffee plant and citrus shows how bees are attracted to the stimulant properties of caffeine in a plant’s nectar. From the plants point of view not only does it attract bees, it sharpens their faculties, so they remember where they have been!
|I wonder if my calomondin orange flower acts as a stimulant|
It is interesting to recall that many plants produce caffeine as a toxin to deter pests. Coffee is a particularly potent killer of slugs! As with many things in life, a little of what is bad for you might do you good. Nature ever so delicately, treads a very fine line.