POLLINATORS: An Introduction
copyright © 2002 k.Ruby
Most people know that plants reproduce through
pollination and setting seed. We are less aware that flowering plants depend
on the services of an insect or animal pollinator to transport the male genetic
material (pollen) to the female reproductive organs of another plant of the
same species. There are many thousands of insect pollinators such as beetles,
butterflies and moths and animal pollinators such as hummingbirds and bats,
but bees (hymenoptera) are the most prolific and efficient of the pollinators.
Their bodies are covered with fine hairs and physical structures designed specifically
for pollen collection. There are over 25,000 species of bees worldwide and 4000
native species counted in the US.
Bees are generally divided into several categories. There are social and solitary bees, generalist and specialist bees. Honey bees are the only truly social bees. They live year round within a social structure, called a colony or hive, with a clear division of labor and they care for their young. The honey bee (apis mellifera) is native to Europe, but has naturalized worldwide.
Bumble bees, some species of which are native to the US, are in the same genus as the honey bee and are considered semi-social. The queen bee builds a seasonal colony which works and lives together during the warm months of food abundance and dies out over the winter (mature bees overwinter in a dormant state waiting to hatch in the next warm season). Bumble bees are important pollinators and have a special relationship to certain plants who will only release their pollon through the strong vibrations of the honey beeës buzz. In particular bumble bees are pollinators for some plants of the Solanaceae family and are often used commercially as pollinators in tomato hothouses.
All the other bees are solitary bees. They
may share nesting areas, but they build and live alone and do not tend their
young once the egg is laid. Among these bees are the mason bees, carpenter bees,
plasterer bees, digger bees and carpenter bees. They range widely in size and
shape and in the manner of building their nests. Nests are commonly built in
snags (dead wood) or directly in the ground and are lined with gathered material
such as leaves or mud. The female bee hatches, mates and sets about building
a nest. For each cell she collects pollen and mixes it with nectar to form a
perfectly round pollen ball. This ball or Ñbee breadì as it is
often called, is deposited into a cell and a single egg is laid on top of it.
The bee then closes the cell and leaves. Nests can range from one to sixty cells,
depnding on the species. Once the egg hatches, the larva eats, poops and pupates.
Depending on the species and the time of year the mature bee will then emerge
and start the cycle over, or over winter in a semi dormant state, waiting for
the right weather conditions. They will often emerge just at the moment that
their prefered host plant is coming into bloom!
Bees offer their pollination "services" for plant "rewards" of pollen and nectar. Some bees are generalists and can gather and claim rewards from a variety of plants. Others are specialists who have developed an evolutionary relationship with a particular plant. Many times their life cycle and physical structures are attuned to this plant in such a way that the two are dependant on eachother for their further existance. If one or the other is endangered both are endangered. Thus if a plant habitat is diminshed in such a way that less bees visit them, pollination does not occur and their seed set is also diminshed. The population may dwindle to the point that bees no longer come to offer their services or die out completely along with their prefered plant. Conversely, if the bee habitat is disrupted, by clearing of dead wood and brush or through constant disruption of the soil through tilling, there may not bee enough bees for effective pollination.
Habitat fragmentation of this sort is a reality in the US. Entire plant species can be destroyed when an area is cleared for a housing project. Fortunately native bees can be quite enduring. Even specialist bees can learn to survive on other plants than their prefered plant. Bees will Çcome back to an area that has been decimated given the right conditions and can exist quite well even in an urban setting given enough of the right kind of habitat. In a recent study by UC Berkeley professors and botanists, 72 native bee species were counted in the Berkeley area alone.
Native bees need much the same things as we do; shelter. food and water. bee habitat can be provided by creatively arranging stumps or other deadwood in your garden and by leaving exposed earth in perenial plant beds unturned. You can also create bee habitat by drilling holes into scrap lumber. Naive bees prefer a range of diameters between 3/16th and 5/16th and between 4 and 8 inches deep. Due to selective color vision bees like flowers in the white, yellow, blue and purple ranges. There are many many native and exotic plants that will draw bees to your yard. Among them are mints, lavenders, yarrow, clarkia, gaillardia, delphinium, poppies, penstamon, milkweed, ceonothus, grindelia, fireweed, verbena and dusty miller. To provide and maintain a regular visiting spot 2 to 3 square meters of plant material seems to be a good minimum. If you provide water in a small pond or bird bath, be sure that there are plenty of landing areas for the bees. Flat rocks or sticks that angle gradually into the water are excellent for this purpose.
Native bees are a vital link in the cycle of life and their role in the continuance of these cycles is often underestimated. Every time a species becomes extinct we loose access to valuable information and wisdom contained in the gene sequence. Gene pool diversity is not only important to human applications, it is valuable in itself. Once that information is lost, we can no longer get it back and we can only wait and see how this loss may effect the entire web of life on the living organism that is this planet. We have a choice to support life or destroy it. Creating habiat for bees and plants is a small part of a bigger solution.
FYI. All female bees ahve the capacity to sting.
No male bees can sting. Most bees, when left to themselves and unthreatened
will not sting. If a bee approaches you, it is possible that you smell good
to them, like a flower! If you walk away calmly and avoid making abrupt movements
you will also most likely avoid a sting.