Honey bees play smaller role in pollination than many believe

With all the recent news concerning honey bee colony collapse disorder, I have been a bit worried about what would happen to the agricultural system that we have in place if this trend were to continue and the honey bees were to die out; so I did some research! In the biology classes I took in school I was led to believe that honey bees were far and away the primary pollinators of flowering plants (angiosperms), and while other creatures such as butterflies and hummingbirds play a somewhat more minor role in pollination, without honey bees humans would be hosed.

We will start with a lesson in basic biology for the nonbelievers among us. Since plants cannot actively move their sexual organs into contact with the corresponding organs of other plants, they must rely on other creatures to take a sperm cell from one and carry it to another plant to fertilize its egg. We will use the standard honey bee to paint an example: a bee lands on a flower (as shown above) and collects a grain of pollen from the flower’s male organ, the anther. After collecting the pollen, this bee will then flit over to another flower and land on it to repeat the process. Since most angiosperms are hermaphroditic, when the bee lands on the next flower it naturally deposits some of the pollen it has collected onto this new flower’s female sexual organ, the stigma. This process allows for the introduction of new genes, which is necessary for the proliferation of the species. The bee then travels back to its hive to store the pollen for later use in the production of honey, which they will use to feed their larva and the adults who can’t go out to forage.

Honey bees are great at fertilizing angiosperms because they are already travelling from flower to flower, and when they land on one the pollen becomes stuck to their hairy abdomens, allowing the bees to carry it with them. There are of course other creatures that travel between flowers and have a means of transporting this pollen, such as the aforementioned hummingbirds and butterflies, but I wanted to know just what portion of the total gets carried out by each kind of critter. In my research I was able to find an amazing article that synthesizes the results of some 39 different studies taking place on five different continents and measure the pollination services provided by honey bees, other types of bees, and non-bee creatures. The results were surprising: on average, honey bees accounted for just 39% of the total flower visits, while other bees made up 23% and non-bees made up 38%. So while honey bees accounted for the largest percentage-or plurality-of visits to flowers recorded, they accounted for an amount that was far from the majority.

The article made a point of specifying that this higher rate of flower visitation did not imply a relatively high rate of pollination, as the rate of pollen deposition was significantly lower than that recorded for any species of bee. So even though non-bees made up a seemingly large portion of the set of total flower visits, the smaller quantities of pollen transported meant that they were not responsponsible for a commensurate portion of total pollination.  The non-bee pollinators included in the article were ants, butterflies, moths, beetles, wasps, and flies, although not included in the study were creatures such as birds, bats,  lizards, and even mammals like lemurs and honey possums that are also known to pollinate some flowers.

One plant-and-creature pair that relies solely on a non-bee means of pollination is the yucca plant and yucca moth, which have formed a symbiotic relationship to ensure their mutual survival that goes back over 40 million years. Evolution has altered the behaviors and physical natures of each species so that one cannot survive without the other. Unlike most breeds of butterflies and moths that have long tongues used to collect pollen from flowers, the yucca moth instead has a collection of tentacle-like appendages that surround its mouth and serve a very important purpose in pollination. The female yucca moth visits the flower of a yucca plant and gathers the pollen produced by some of the anthers of said plant, which it forms into a ball and holds with its mouth tentacles. She then travels to the flower of a different yucca plant and visits the stigma, where she not only deposits the ball of pollen but also lays her eggs. When these eggs hatch, the larva will feed on the fruit and seeds of the fertilized flower until it is fully grown, at which point it drops to the ground and digs into the earth to build a cocoon where it will stay until the next spring, when it emerges to start the process all over again.