Friday, August 2, 2013

Bee-utiful: honeybee pollination of our favorite foods

Enjoying your summer fruits and veggies? Thank the bees!

some favorite fruits, nuts, and veggies pollinated by bees
image: Operation Bee
Here’s why:

As they buzz from flower to flower, bees pollinate roughly 71 of the 100 fruit, vegetable, nut, and other crop plant species that provide 90% of the world’s food, according to the United Nations Food and Agriculture Organization (FAO).

This includes not only fruits, nuts, and veggies, but also alfalfa and other plants that are key to livestock production.

In fact, crops pollinated by bees comprise roughly one-third of our diet (here's a list of crop plants pollinated by bees), yet their requirements and their massive contribution to agricultural production have mostly gone unnoticed until recently, when bee colonies across the U.S. and Europe started failing.

More on the disappearance of bees in a future post - this one discusses bee fitness and pollination.

Why do bees visit all these plants?

You probably already know that honeybees gather sugary nectar from flowers to make honey, which gives them (and us!) quick energy. But did you know that they also collect pollen, which is basically a powder that contains the male reproductive cells of seed plants?

Honeybees are social insects, and the many thousands of female worker bees that forage from a single honeybee colony can contact many thousands of flowers in a day.

honeybees eating...honey!
photo: P.O. Gustafson
They make honey from nectar, which workers suck up from flowers with their long proboscis/tongue.

The nectar actually goes down to a bee’s extra stomach, called a honey stomach, where it begins to reform into fructose and sucrose that make up the honey.

Back at the hive, the bee regurgitates the reformed nectar/honey (yes, the bee vomits up the honey) to other bees as food or so they can refine it (yes, they keep digesting and regurgitating it). They then either eat it or store it in cells of the honeycomb (made from beeswax) for future use.

Honeybees store the honey for use during the cold winter months when there are no flowers. They stay active all winter and eat their stored honey to produce body heat. The tens of thousands of bees buzzing around a given colony keep the hive warm and evaporate the water, concentrating the honey and giving it long shelf life.

Depending on the length and severity of the winter, a colony can consume 15 to 50 kg (30 to 100 pounds) of honey during the cold season. While many species of bees and other insects eat (drink?) nectar, only a few concentrate it to make honey.

honeybee carrying pollen
photo: Muhammad Mahdi Karim, Wikimedia

Honeybees collect the pollen because it contains protein and nutrients, which the bees mix with water and either eat or feed to their developing larvae. Bumblebees do the same, but they shake down plants for pollen by vibrating rapidly, creating their tell-tale buzz.

What’s in it for the plants?

honeybee on a willow
photo: Bob Peterson, Wikimedia
While the pollen of some major cereal crops, such as wheat and rice, is distributed by wind, most plants with seeds depend on animal pollinators, most frequently bees, to reproduce.

As they move from plant to plant, bees get pollen all over their hairy bodies and end up distributing some of their pollen (which you will recall, contains male reproductive cells) among the female reproductive structures (flower pistils, or cones of conifers) of the many plants they visit.

Bees tend to transfer pollen among plants of the same species, perhaps because of the high likelihood that many plants of a given species will have flowers at the same time. By bringing male and female flower parts together, their visits pollinate, or fertilize, flowers. As unlikely as this sounds for a reproductive strategy, it works.

As you can see, the biological fitness levels of many bees and seed plants are linked: bees require nectar and pollen for energy and growth, and plants depend on bees and other animals to fertilize their seeds.

Symbiosis and the importance of pollinators for specific plants

on left: what happens when pear trees aren't sufficiently pollinated
photo: Canada Agriculture Musuem
A recent experimental study showed that the loss of bees can affect plants’ ability to reproduce. The researchers noted that when the most populous bee species was removed from plots, other bee species stopped specializing in a particular flower, in this case, the larkspur, and carried around pollen from various flowers. This lowered pollination rates for larkspur plants because bees were now carrying other species’ pollen to them, which was, of course, not very helpful.

Here’s the abstract and the full paper for those really interested!

Like many natural phenomena, the value of the pollination services provided by bees, bats, birds, butterflies, and beetles, as well as the consequences of losing them, are not typically considered in economic valuations of the use of chemicals or the conservation of native forests and grasslands.

That discussion is for another post!

Learn more about bees!

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