|
06-12-03
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!
|
