TIME: Almanac 1993/TIME Almanac 1993.iso/time/081092/0810300.000

Text File | 1993-04-08 | 12.5 KB | 258 lines

                                                                                SCIENCE, Page 46

Summer's Bloodsuckers


In the fight against 100 trillion mosquitoes, the tactics are
changing. The new motto: Know your enemy.

By HENDRIK HERTZBERG/GAINESVILLE


    It is your trump,
    It is your hateful little trump,
    You pointed fiend,
    Which shakes my sudden blood to hatred of you:
    It is your small, high, hateful bugle in my ear.
    Why do you do it?
    Surely it is bad policy.
    They say you can't help it.

    -- D.H. Lawrence, The Mosquito


    Sometime this summer -- it's probably already happened --
you will hear that hateful little trump. At the first sound of
its intensely annoying whiny hum, faint but frantically
high-pitched, you'll hold stock-still, on full alert, hand
raised at the ready. And then: splat. One less mosquito to
trouble the peace of man and beast.

    As you brush aside the spindly corpse, the poet's question
may occur to you. Why do mosquitoes make that irritating little
noise? Its usefulness from the human point of view is obvious.
But what is its survival value from the mosquito point of view?
Why in the world would these otherwise canny creatures go to the
trouble of evolving a behavior so ideally suited to helping
their prey find and swat them?

    A good place to ponder this puzzle -- or to find out
anything else you ever wanted to know about mosquitoes -- is an
innocuous-looking brick building near the University of
Florida's Gainesville campus. Its halls nourish, among other
obscure yet useful twigs of the mighty oak that is the U.S.
government, the Mosquito Unit, or, as it is formally known, the
Mosquito and Fly Research Unit at the Medical and Veterinary
Entomology Research Laboratory of the Agricultural Research
Service of the U.S. Department of Agriculture.

    This bastion of research in the battle against bugs has
never been more important. A new enemy has appeared in the form
of the Asian tiger mosquito, a variety that was accidentally
imported from Japan in 1985 and has since spread to 21 states,
mostly in the Southeast. Government scientists announced last
month that a group of these mosquitoes in Florida had been found
to be carrying the virus for Eastern equine encephalitis, a
rare but often fatal brain disease. Only 11 Floridians have
caught this disease, and health officials see no reason for
panic, but mosquito control has taken on a new urgency.

    Gainesville's Mosquito Unit, along with everybody else
involved in what is anthropocentrically called pest control, is
rethinking its philosophy and strategy. The mosquitoes are the
same, crafty and cunning as ever. But the weapons and tactics
used to combat them are changing fast. Chemicals are out;
biologicals are in. Dumping poisons indiscriminately is no
longer in vogue; figuring out ecologically correct ways to get
mosquitoes to do themselves in is all the rage. "The era of
insecticides is coming to an end," says Donald Barnard, the
Mosquito Unit's chief. "They're still our first line of defense.
But the bugs adapt very quickly to whatever we throw at them.
The emphasis now is on outsmarting them, and to do that you have
to understand their behavior."

    Very well: Why do mosquitoes whine? For many species, the
unit's two dozen scientists and technicians will answer in one
voice, and in one word: sex.

    A mosquito, it seems, is essentially a tiny winged speck
of libido. Here's what typically happens: the males form a
hovering globular swarm, ranging from a softball-size band of
a dozen to a ballroom-size throng of millions. To any female
that may be around, the male buzzing sound is like a neon sign
in front of a singles bar. She makes a beeline -- all right, a
mosquitoline -- straight into the swarm. Once she's inside, the
sound of her wings, beating 250 to 500 times a second, becomes
the mosquito equivalent of a flirty hair flip. The males
frantically elbow each other to get at her, and within seconds
one of them scores. The pair, copulating in midair, float down
in crazy circles, coming briefly to rest in a tangle of legs and
antennae. Who cares if that hum might later cost them their
lives? It was worth it.

    Among mosquitoes, by the way, the "woman above" position
is mandatory. Their sexual organs are weirdly like ours, with
vaginas, ovaries, penises and testes. Their coupling takes four
to 40 seconds, though in a few of the 2,500 known species male
and female may remain locked together for more than an hour.
They show every sign of ecstasy, but do they feel it? Mosquito
Unit head Barnard looks pained. This is not the sort of
question sober scientists are supposed to concern themselves
with, and besides, there's nothing in the literature about it.
"Well," he finally admits with a sigh, "they do have a central
nervous system."

    The sex had better be good, because in most mosquito
species that have been studied it's strictly a one-night stand.
The female has no further need of her partner or any other male
for the rest of her life. She stores the sperm from her sole
encounter in special sacs, fertilizing her own eggs every time
she lays a batch, whether that is once or a dozen times.

    From this point on, in any case, sex no longer rules her
life; violence does -- and this is where we come in. To nourish
and develop her eggs, she needs what entomologists call, with
admirable directness, a "blood meal" -- and she needs a new one
for every batch of eggs she lays. Every mosquito bite in the
history of life on earth has been inflicted by a female. This
is science, not misogyny.

    When a blood-hungry mosquito lands on a human forearm --
or, more likely, on the eyelid of a cow, the haunch of a
squirrel, the wing of a roosting bird or even the back of a
caterpillar -- she goes to work with awesome efficiency. Her
slender proboscis, consisting of two sharp and sometimes
serrated cutting tools surrounding a pair of tiny tubes, pierces
the skin (and, if necessary, the cloth or feathers protecting
it) and finds a capillary, bending to slide into the tiny blood
vessel. Down one tube comes her saliva, which deadens sensation
and blocks coagulation. Up the other goes a drop of her victim's
blood. In less than a minute, she makes her getaway. She finds
a place to rest and digest her vampire's repast, while her
victim is left to scratch the welt that soon forms in allergic
reaction to her ghoulish drool.

    The eggs she will lay a few days later -- from half a
dozen to upwards of 300, depending on her species and the
richness of her blood meal -- turn into larvae, which lead a
complete aquatic life of their own and are as different from
flying mosquitoes as seals are from buzzards. Not much water is
needed: a tablespoon in an old beer can or tire casing is enough
to provide a home for 200 of these little air-breathing water
worms, but the more water the better. The larvae zip around,
feeding on bacteria and bits of vegetation, which they filter
through bristles in their mouths. In some species they also eat
one another or the larvae of other mosquitoes, a habit the folks
at the Mosquito Unit would like to encourage.

    After a set time -- from less than a week to several
months, depending on the species -- the larva suddenly stops
eating, curls up into a comma and becomes what is called a pupa.
Over the next few days, it transforms itself like some buggy
version of Terminator 2. Its nerves and muscles melt and reform
with astonishing speed until the new adult mosquito sloughs the
pupal skin, emerges at the surface and takes off. If one thinks
of the humble, fishy mosquito larva as a distinct animal in its
own right, then it is one of God's creatures for which
resurrection and afterlife are scientific facts. Instead of
dying, it sprouts wings and ascends into the heavens.

    Once airborne, the mosquito becomes a flying machine that
puts state-of-the-art aeronautics to shame. Mosquitoes have
range: though most live out their lives within a radius of a
kilometer or two, some swamp species have been known to fly more
than 160 km (100 miles). And they have maneuverability: a
mosquito flying through a rainstorm can land safe and dry on the
nape of your neck after dodging hundreds of drops that to it
are as big as falling refrigerators.

    All this makes the mosquito a formidable adversary, one
that has caused no end of trouble for human beings. Malarial
mosquitoes, some historians think, contributed to the fall of
ancient Greece. Europeans of medieval times were tormented by
the insect Chaucer knew as the midge; the English word mosquito,
from the Spanish for "little fly," appeared in the 16th century,
along with new and nastier New World species. In the 1880s the
Frenchman Ferdinand de Lesseps, fresh from the triumph of
building the Suez Canal, was utterly vanquished in his heroic
effort to dig a canal across the Isthmus of Panama, partly
because thousands of the Europeans he brought with him fell
victim to mosquito-borne disease.

    With the deployment of DDT in 1939, it looked as if final
victory over the mosquito might be at hand; and indeed, through
the years chemical insecticides took such a toll on mosquito
populations that yellow fever and other infections they carried
became almost unheard-of in the developed world.

    Chemicals also took a toll on mosquito research. "The age
of DDT was also the dark age of entomology," says Dan Kline,
another of the Mosquito Unit's scientists. "There was no money
for basic research. Mosquitoes a problem? Just take some DDT and
nuke 'em. Why bother with research when you can do that?"

    The quest for new methods of mosquito control has turned
the dark age into something of a golden age. Government
scientists such as Barnard and Kline now have strong arguments
for spending less of their time testing bug-killing chemicals
and more of it trying to understand the way mosquitoes behave
and how they fit into the great chain of being.

    This change reflects more than the growing reluctance to
put powerful poisons into the environment, where they can make
their way into human and animal tissues. Insecticides are
fearsome engines of natural selection. A dose of strong
insecticide will kill every mosquito it touches -- every one,
that is, except those that are immune because of some genetic
quirk. The resistant bugs, left alive to reproduce themselves,
eventually come to dominate the species. Chemical insecticides
are great at suppressing bug populations in the short run, but
over time they are just a particularly efficient method of
breeding tougher, hardier insects.

    Seeing the ultimate futility of spraying chemicals all
over the landscape, pest controllers are looking at ways to
lure mosquitoes into traps that poison the bugs without
contaminating the whole environment. One idea is to copy the
buzzing sound of the mosquito's sexual come-on. Another
technique is to discover and duplicate the chemical odors that
attract mosquitoes to animals. Possible bait: octonol, a
compound in cow's breath. A third set of strategies turns on the
attractant qualities of heat, which mosquitoes like. (If your
hot-blooded spouse wakes up covered with bites and you don't,
his or her slightly higher body temperature may be to blame.)

    A better way to conquer mosquitoes may be to enlist their
natural enemies. The Mosquito Unit's experts think bug
populations could be infected with -- and decimated by -- a
variety of microbes, including protozoans and fungi.
Entomologist Jimmy Becnel expects to conduct a field test of
such biological warfare within a year or two.

    Genetic engineering could one day be the best weapon.
Scientists hope to create mutant strains of mosquitoes that do
not lay eggs or at least do not nourish them in the usual
bloodsucking fashion. Introducing the mutants into mosquito
populations could lead to interbreeding and thus interfere with
the rampant reproduction of the natural bugs.

    But the battle between man and mosquito has been raging
for a long time, and neither side is likely to win it soon.
Despite all of man's spraying, draining, zapping and slapping,
there are still an awful lot of mosquitoes in the world. Nobody
knows how many, but a very rough calculation (the only kind
possible) would put the total number of mosquitoes on the planet
at any given moment at around 100 trillion, give or take a few
dozen trillion. So you needn't feel too bad about squashing a
few.