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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!
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