To celebrate Australia’s first Pollination Week, kicking off on November 15, we’re sharing a sneak peak at one of the articles in Pip #4, where native bee expert Megan Halcroft takes us on a fascinating journey into the solitary world of Australia’s bees.
Bees are under threat worldwide. As we urbanise our environments we remove bees’ natural habitat – we create flowerless landscapes when we substitute concrete and lawn for flowering trees and shrubs. And agricultural practices, such as monoculture, remove the variety of floral resources bees need for good health. Add to these the increasing use of pesticides in crop management and domestic landscapes, and the future for bees looks bleak.
Mention bees and people invariably think of honey bees. Humans have had an important relationship with honey bees for millennia, managing them for honey and pollination
services. The social European honey bee Apis mellifera can be found in most parts
of the world, and was introduced into Australia in 1822; however, this species is only one of 20 000 species of bees worldwide. Australia is home to almost 2000 species of native bees, and most of them are very important plant pollinators. We can support native bee health and populations by improving our understanding of bee behaviour, and how that drives biodiversity. And understanding the importance of bees is
about understanding pollination, which facilitates plant sexual reproduction, and the bees’ role in it: biodiversity relies on mixing in the gene pool.
FLOWERING PLANTS AND BEES COEVOLVED
Around 100 million years ago, flowering plants (angiosperms) began to evolve. During this time, some wasps began to collect pollen as a protein source to rear their offspring (brood) instead of feeding them other insects; a complex coevolutionary system developed. Plants are immobile therefore unable to move about to find a mate, and this is where pollination vectors such as insects play an important role. Plants have evolved ways of attracting pollinators to their flowers by enhancing the sugar concentration in their nectar, producing attractive scents and colours, and providing nectar guides to help insects find the food source. This, in turn, helps the plant to reproduce. Pollination is the transfer of pollen from the anther (male flower structure) to the stigma (female flower structure). The stigmatic surface is highly nourishing and stimulates pollen germination.
As the pollen tube grows, it carries the male gamete towards the female gamete, within the ovule. Gamete union is called fertilisation, which leads to seed set and results in the production of a plant hormone that stimulates fruit tissue development. So, good pollination produces good fruit quality and yield. Seed produced through good pollination has superior germination qualities.
Of the 2000 Australian bee species fewer than fifteen are highly social and colony-forming. Most species are solitary and do not make honey, but they are very important pollinators. Female bees are experts at collecting and transporting pollen and nectar back to their nests, to rear brood. Most bees are covered with branched, electrostatic hairs, to which pollen grains are attracted. Females have specially adapted structures for transporting pollen, called scopa. Some species have stiff bristles under the abdomen where dry pollen grains are packed, while others – such as blue banded and teddy bear bees – have scopa on the outside of the hind leg, or on the inside of the hind legs and the abdomen.
One of the most important aspects of these scopal hairs is that they carry millions of dry pollen grains. These are available for transfer from one flower to another as female bees move over the flowers. Solitary bees live their lives independent of
other bees in various nesting substrates. Once a female has mated, she finds a safe nesting place to rear her brood. She forages for floral resources, returns to the nest, unpacks the pollen from her scopa and regurgitates swallowed nectar. She combines these resources into ‘bee bread’,lays an egg on top, seals the brood cell and leaves the egg to develop alone. This process is repeated many times, until she dies. As she collects her precious cargo of pollen and nectar she performs pollination services.
Want to keep reading for Megan’s practical tips on attracting native bees to your garden? Subscribe to Pip Magazine!
Megan Halcroft is a scientist specialising in research on Apis australis – the Australian native bee. To see more of her work visit: www.beesbusiness.com.au. To find out more about Pollinator Week events, join their Facebook Group.