JUNE
2003

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

06-12-03

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

In Mosquitoes, the Lady is a Vamp


It is safe to say that almost everybody dislikes mosquitoes. To be sure, a fair number of people make a living because of mosquitoes. We're talking about folks like scientists who study them, pest control specialists who try to get rid of them and manufacturers who make things to kill them. But to most of us, mosquitoes are the worst of the pest insects; we would just as soon they didn't exist.

As a group, mosquitoes have earned the right to be called the number one insect pest of all time. Mosquitoes can kill us. Not directly, but by transmitting organisms that cause disease. It has been estimated that mosquito-borne diseases have resulted in more human deaths than all the wars in the history of the world.

Mosquitoes are vectors for malaria, yellow fever and dengue. They also transmit viruses that cause encephalitis and West Nile. Nematodes responsible for elephantiasis get into humans because of mosquito bites.

Yes, it is the bite of the mosquito that is the basis for our rightful disdain for this insect. Aristotle recognized the danger in the bite of Diptera, including flies and mosquitoes, when he wrote, "Four winged insects (the bees) have the sting in the tail, and the two winged ones (the Diptera).have the sting in the front of the head."

An old African folktale also focuses on the bite of the mosquito in the story of "Why Mosquitoes Buzz in People's Ears." This tale explains why people react with a slap when they hear the buzz of a mosquito. The African tale relates the reaction to a lingering bias toward the insect because of havoc caused in the past. To most folks, hearing a mosquito buzz is an indicator of things to come--of bad things to come, like a mosquito bite!

So while our human history with mosquitoes is one of disease and death, our individual experiences are of bites that hurt and turn into itchy, red welts. Not all mosquitoes hurt when they bite. Some species manage to get a blood meal without the human donor taking notice. Other species, however, get our attention when they bite.

Whether we can feel them or not, the goal of the mosquito when biting is to ingest blood. For the mosquito, the blood meal is a matter of survival for the species. These insects need blood to produce eggs. Since egg production is involved, the blood-feeding mosquito is always a female. Yes, it is the female mosquito that bites! Male mosquitoes do not bite, even though we might hear them buzzing around at times.

So how does this biting work? First, the female mosquito that is in need of a blood fix is attracted to a living, breathing animal. It is the temperature of the animal and the carbon dioxide in exhaled air that serve as attractants. If the potential vamp is able to land, it will insert its mouthparts into the skin.

Once the mosquito gets its stylets--that's what scientists call the needle-sharp parts of the mouthpart--into the skin, it injects saliva. The saliva contains chemicals that prevent the blood from clotting and is what causes the itching following the bite.

The mosquito will feed until she is filled with blood. If she doesn't get the necessary amount from one animal, she will go to another. Since mosquitoes sometimes feed on many hosts that means they can pick up the disease organism from one animal and carry it to another. That is why in discussions of mosquito-borne diseases, like yellow fever and West Nile, there is a discussion of reservoirs.

Reservoirs are species that harbor the disease organism. Mosquitoes carry the disease organisms from the reservoir to the human. That is where the nasty little female mosquito vamps come in. And to add insult to injury, those little mosquito vamps hum while they work!

 

 

Writer: Tom Turpin
Editor: Olivia Maddox