Friday, 17 July 2015

Pollinator ID for Botanists: an introduction

Pair of mason bees on Charlock Sinapis arvensis.
Female has pollen-collecting hairs beneath the abdomen;
male lacks these hairs & doesn't collect pollen.
Image: R. Clark

 
This is the final day of national Pollinator Awareness Week and many of us who have been out botanising have become very aware of our lack of pollinator ID skills! 

Fortunately BSBI botanist Ryan Clark, who co-ordinates our annual New Year Plant Hunt and sits on BSBI Meetings & Communications Committee, is also an entomologist with a particular passion for pollinators

A recent graduate, his BSc dissertation was on using plants to conserve pollinators.

Ryan has very kindly put this guest blogpost together for us:

Pollinator ID for Botanists: an introduction.

Male leafcutter bee, showing
the typical resting position,
with wings outstretched.
Image: R. Clark
With about 87% of the world’s flowering plants relying upon insect pollination to reproduce, pollinators play a vital role in terrestrial ecosystems. 

In 2013, the State of Nature report [to which BSBI was a contributor - Ed.] was launched; the report estimates that over two thirds of our invertebrate species have declined over the last fifty years, including many of the orders of insects that can act as pollinators. 

Approximately 58% of our flowering plant species have also declined over the same time period, with specialist plants and pollinators worst affected. 

In Britain there are a number of groups of insects that can act as pollinators of the plants that we all know and love including bees, hoverflies, moths, butterflies, beetles and other flies. Pollination is accidental from the insects' perspective and most insects, including beetles and wasps, have the capabilities to carry pollen between plants.  

Bees
A female mining bee, showing that this group
collects pollen on the hairs on their hind legs.
Image: R. Clark
Bees are arguably the most important pollinators in Britain and are also the group of pollinators that are most in trouble, facing widespread declines in both population and distribution. 

When people think of bees they often think of the honey bee, an arguably non native species, or bumblebees. Solitary bees, however, are often overlooked and make up around 80% of the 250 bee species found in Britain. 

Honey bees are effective pollinators but only due to the numbers in which they are found in Britain, with bumblebees and solitary bees being much more effective at pollination. 

A hoverfly pretending to be a
bumble-bee! Note how the eyes &
 wings are different from bees.
Image: R. Clark
Like honey bees, bumblebees are social, with colonies, comprising one queen and lots of worker bees (also females), which break down, with new queens and males produced. 

Solitary bees - as the name suggests - usually live alone and collect pollen to provision their own young only and they are smaller than bumblebees. The main types of solitary bees that you are likely to see are miner bees (Andrena species), leafcutter bees (Megachile species) and mason bees (Osmia species), all of which are effective pollinators. 

Miner bees in the genus Andrena nest usually in the ground, digging a tunnel and laying eggs in there, provisioning the young with a mix of nectar and pollen. Most of these bees are rather large and chunky and they collect pollen on their hind legs. 

On the other hand mason bees, Osmia species collect pollen on the underside of their abdomens. Similarly, leafcutter bees also collect pollen on the underside of their abdomens and, with their wings outstretched, are distinctive when at rest . 

For more information on different types of bees in Britain, please follow this link

Hoverflies
Marmalade hoverfly on Viper's-bugloss
Echium vulgare
Image: R. Clark
Hoverflies are also rather efficient pollinators and are thought to be undergoing dramatic declines, but we know even less about these declines than we do for bees! There are around 270 hoverfly species found in Britain, nearly all of which visit plants for nectar and therefore carry pollen from one plant to another. 

Hoverflies are best noticed by their hovering action in midair, although this trait is shared with some other fly groups and often mimic bees.Their eyes are different though and they have no way of purposefully carrying pollen on their bodies. Flies also appear to have one pair of wings, whereas bees have two. 

Beetles are also important pollinators:
seen here on Bramble Rubus sp.
Image: R. Clark 
I plan to write a more detailed guide to hoverflies later this week, so keep an eye on my blog here. I should also point out that, although less showy than hoverflies, other fly families are also remarkable pollinators, they are just not studied as well in Britain.

Butterflies and Moths
We are all familiar with butterflies and day flying moths visiting flowers by day and carrying pollen between plants, but what about at night? 

There are a remarkable 2500 species of moth in Britain ranging in size from a few mm long to over 10cm long and they are busy pollinating plants while we sleep. Some plants have even adapted to release scents at night to attract these wonderful insects. Moths are even thought to pollinate some orchids