JULY
2003

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

07-24-03

Insect Odors Worth a Thousand Words

Insects communicate in a variety of ways. To be sure, insects don't read and write as do many humans. But insects are able to get their message across anyway.

Some insects produce sound for the purpose of communication.  Humans have long admired the acoustical abilities of insects. Even poets are moved to pen a few lines to sound-producing insects like crickets, katydids and cicadas.

A few insects use light to send a message. Almost everyone has seen or heard of the insects called fireflies or lightning bugs. These beetles use a series of light flashes to communicate with each other.

One of the most common approaches to communication among insects is the use of odor. Odors are used by a variety of animals and plants to send messages. Think about the perfume of flowers or the stench produced by a skunk when disturbed!

So how do insects use odors to communicate? Sometimes the odor is used, like a skunk, to gain protection. The stink bug has a name that reflects its use of a bad odor to discourage would-be predators. Anyone who has picked up a stink bug knows that this insect releases a bad smelling, and tasting, chemical under those circumstances.

Ladybugs do the same thing. When handled, these bright-colored insects release a foul chemical through their leg sockets, as anyone who has captured a ladybug knows. That process is known as reflex bleeding, and, like the stink of the stink bug, helps the insect protect itself.

Insects also use odors to attract mates. The French naturalist Jean-Henri Fabre concluded that a female moth released an odor that is attractive to the opposite sex. The basis for his observation was a female peacock moth that had emerged from a cocoon in his laboratory. Within hours, dozens of male moths were attracted to the cage that contained the female. No matter where Fabre moved the female, the males discovered her.

Since the 1870s when Fabre made his observations, hundreds of insects have been shown to produce chemicals used to attract the opposite sex. The first identification of one of these mate-attracting insect chemicals was made by a German scientist. Adolph Butenandt made the discovery by grinding up the tips of the abdomen of female silkworm moths and presenting various extracts to male moths. The substance that excited the male moths was a kind of alcohol. Butenandt named the chemical bombykol, after the silkworm moths Latin name, Bombyx mori.

Today, chemicals that cause a response in other members of the same species are called pheromones. The word pheromone is from the Greek "carrier of excitement." It is probably no accident that a human perfume is called "Pheromone!"

Not all insect pheromones are used to attract mates. Some are used as trail marking substances by ants. Pheromones are used to maintain the caste system in ants, bees and termites.

Honey bees use pheromones to induce nestmates to sting animals that disturb their nests. Humans can smell this honey bee pheromone. Seasoned beekeepers know that a whiff of this chemical means the bees are getting mad.

A pheromone is designed to send a message to members of the same species. But in the case of the honey bee alarm pheromone, its presence also sends a two-word message to beekeepers - get out!

 

Writer: Tom Turpin
Editor: Olivia Maddox