JANUARY
2011

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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01-27-11

Download the audio of On Six Legs: MP3, WMV.

Insect Pollinators Will Work for Food


bumble bee

What is pollination? One way to find out is to look up the definition of the word. It is just for such situations that we have dictionaries. Today you can go online to find a word definition or consult a printed text. Historically, there have been several publishers of dictionaries including the one that Rowan and Martin deadpanned about in the late-1960s TV comedy show "Laugh-In." Faced with the need to explain a word they would say, "Look that up in your Funk & Wagnalls." I don't have a Funk & Wagnalls, but according to my American Heritage dictionary the definition of pollination is "to convey or transfer pollen from an anther to a stigma of a flower in the process of fertilization." Like a lot of definitions, that one is, well, a bit dull.

To biologists, pollination is a process, a complex part of sexual reproduction in plants. The pollination system has evolved over millions of years and involves specialized plant structures and transportation of pollen by mechanical means or by living organisms. It is also a tale of bribery and sometimes deceit fitting for a tell-all TV talk show.

Plant pollination takes place under our very noses on a daily basis during the growing season, but mostly to indifferent spectators. Except, that is, to the 30 percent or so of us who suffer from allergic rhinitis, a respiratory ailment better known as hay fever. This is a disease that is often caused by the inhalation of pollen grains.

So how did insects get involved in plant pollination? No one knows for sure, but one hypothesis is that it all began when some ancient beetles discovered that pollen was a good food item. Why beetles and not some other type of insect? As it turns out beetles have been on the earth for a long time and were here before plants even had flowers. In addition, beetles have mouthparts of the chewing type that would have made it easy for them masticate and ingest pollen.

What happened after this is an example of what scientists call coevolution. Coevolution is when two organisms have evolved to a point where both are dependent on the other for survival. An example of such a system is some flowering plants and insects that transport pollen.

Here's how it works. Plants produce pollen that needs to be transported to other plants for sexual reproduction to be successful. The plant has a flower that is an attraction to insects because of its odor and ultraviolet color patterns. The flower is also a convenient landing pad.

Insects visit flowers because of the availability of a sip of nectar, a food item for the insect. The structure of the flower is such that the insect will get pollen on its body as it works its way to the source of the nectar. The sip of nectar is small enough so that the insect goes from flower to flower in order to satisfy its hunger. When that happens pollen from one flower is transferred to another by the insect. The result is that the plants are pollinated and the insects get fed. It's a "You scratch my back and I'll return the favor" type of system that is very popular in the political world.

On the insect side of the deal the best pollinators normally have the ability to fly, have mouthparts structured to imbibe nectar and a hairy body good for collecting pollen. Insect pollinators include a few beetles, some butterflies and moths, a few flies, a few wasps and a lot of bees.

Most plant pollination by insects is due to bees where the pollen, and sometimes the nectar, becomes a food source for the adults and the immature forms. The bee pollinators include those called solitary bees because they each have their own nests. Some like sweat bees and mining bees live in ground burrows. Others such as orchard bees and carpenter bees live in wood cavities.

The most recognizable of the bees are social bees that live in colonies. These are bumble bees that have an annual colony and honey bees that live in a colony that persists over several years.

Pollination seems like a great system where everyone wins. Not so. A few bumble bees are known as nectar thieves. They chew through the flower and steal the nectar without carrying pollen. Now that's a real slap in the face of your honey!

 

Writer: Tom Turpin
Editor: Olivia Maddox