338 lines
16 KiB
Markdown
338 lines
16 KiB
Markdown
---
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created_at: '2014-09-29T19:27:32.000Z'
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title: A world without mosquitoes (2010)
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url: http://www.nature.com/news/2010/100721/full/466432a.html
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author: denzil_correa
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points: 92
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story_text: ''
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comment_text:
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num_comments: 60
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story_id:
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story_title:
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story_url:
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parent_id:
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created_at_i: 1412018852
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_tags:
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- story
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- author_denzil_correa
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- story_8384709
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objectID: '8384709'
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year: 2010
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---
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Published online 21 July 2010 | Nature 466, 432-434 (2010) |
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doi:10.1038/466432a
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News Feature
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Eradicating any organism would have serious consequences for ecosystems
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— wouldn't it? Not when it comes to mosquitoes, finds Janet Fang.
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Every day, Jittawadee Murphy unlocks a hot, padlocked room at the Walter
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Reed Army Institute of Research in Silver Spring, Maryland, to a swarm
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of malaria-carrying mosquitoes (Anopheles stephensi). She gives millions
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of larvae a diet of ground-up fish food, and offers the gravid females
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blood to suck from the bellies of unconscious mice — they drain 24 of
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the rodents a month. Murphy has been studying mosquitoes for 20 years,
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working on ways to limit the spread of the parasites they carry. Still,
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she says, she would rather they were wiped off the Earth.
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That sentiment is widely shared. Malaria infects some 247 million people
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worldwide each year, and kills nearly one million. Mosquitoes cause a
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huge further medical and financial burden by spreading yellow fever,
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dengue fever, Japanese encephalitis, Rift Valley fever, Chikungunya
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virus and West Nile virus. Then there's the pest factor: they form
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swarms thick enough to asphyxiate caribou in Alaska and now, as their
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numbers reach a seasonal peak, their proboscises are plunged into human
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flesh across the Northern Hemisphere.
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So what would happen if there were none? Would anyone or anything miss
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them? Nature put this question to scientists who explore aspects of
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mosquito biology and ecology, and unearthed some surprising answers.
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There are 3,500 named species of mosquito, of which only a couple of
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hundred bite or bother humans. They live on almost every continent and
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habitat, and serve important functions in numerous ecosystems.
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"Mosquitoes have been on Earth for more than 100 million years," says
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Murphy, "and they have co-evolved with so many species along the way."
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Wiping out a species of mosquito could leave a predator without prey, or
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a plant without a pollinator. And exploring a world without mosquitoes
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is more than an exercise in imagination: [intense efforts are under
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way](http://www.nature.com/news/malaria-control-the-great-mosquito-hunt-1.15524)
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to develop methods that might rid the world of the most pernicious,
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disease-carrying species (see ['War against the
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winged'](/news/2010/100721/full/466432a/box/1.html)).
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Yet in many cases, scientists acknowledge that the ecological scar left
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by a missing mosquito would heal quickly as the niche was filled by
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other organisms. Life would continue as before — or even better. When it
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comes to the major disease vectors, "it's difficult to see what the
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downside would be to removal, except for collateral damage", says insect
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ecologist Steven Juliano, of Illinois State University in Normal. A
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world without mosquitoes would be "more secure for us", says medical
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entomologist Carlos Brisola Marcondes from the Federal University of
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Santa Catarina in Brazil. "The elimination of Anopheles would be very
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significant for mankind."
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## Arctic pests
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Elimination of mosquitoes might make the biggest ecological difference
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in the Arctic tundra, home to mosquito species including Aedes impiger
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and Aedes nigripes. Eggs laid by the insects hatch the next year after
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the snow melts, and development to adults takes only 3–4 weeks. From
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northern Canada to Russia, there is a brief period in which they are
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extraordinarily abundant, in some areas forming thick clouds. "That's an
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exceptionally rare situation worldwide," says entomologist Daniel
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Strickman, programme leader for medical and urban entomology at the US
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Department of Agriculture in Beltsville, Maryland. "There is no other
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place in the world where they are that much biomass."
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> “If there was a benefit to having them around, we would have found a
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> way to exploit them. We haven't wanted anything from mosquitoes except
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> for them to go away.”
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Views differ on what would happen if that biomass vanished. Bruce
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Harrison, an entomologist at the North Carolina Department of
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Environment and Natural Resources in Winston-Salem estimates that the
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number of migratory birds that nest in the tundra could drop by more
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than 50% without mosquitoes to eat. Other researchers disagree. Cathy
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Curby, a wildlife biologist at the US Fish and Wildlife Service in
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Fairbanks, Alaska, says that Arctic mosquitoes don't show up in bird
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stomach samples in high numbers, and that midges are a more important
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source of food. "We (as humans) may overestimate the number of
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mosquitoes in the Arctic because they are selectively attracted to us,"
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she says.
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Mosquitoes consume up to 300 millilitres of blood a day from each animal
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in a caribou herd, which are thought to select paths facing into the
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wind to escape the swarm. A small change in path can have major
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consequences in an Arctic valley through which thousands of caribou
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migrate, trampling the ground, eating lichens, transporting nutrients,
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feeding wolves, and generally altering the ecology. Taken all together,
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then, mosquitoes would be missed in the Arctic — but is the same true
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elsewhere?
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## Food on the wing
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"Mosquitoes are delectable things to eat and they're easy to catch,"
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says aquatic entomologist Richard Merritt, at Michigan State University
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in East Lansing. In the absence of their larvae, hundreds of species of
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fish would have to change their diet to survive. "This may sound simple,
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but traits such as feeding behaviour are deeply imprinted, genetically,
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in those fish," says Harrison. The mosquitofish (Gambusia affinis), for
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example, is a specialized predator — so effective at killing mosquitoes
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that it is stocked in rice fields and swimming pools as pest control —
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that could go extinct. And the loss of these or other fish could have
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major effects up and down the food chain.
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Many species of insect, spider, salamander, lizard and frog would also
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lose a primary food source. In one study published last month,
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researchers tracked insect-eating house martins at a park in Camargue,
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France, after the area was sprayed with a microbial mosquito-control
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agent[1](#B1). They found that the birds produced on average two chicks
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per nest after spraying, compared with three for birds at control sites.
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Most mosquito-eating birds would probably switch to other insects that,
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post-mosquitoes, might emerge in large numbers to take their place.
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Other insectivores might not miss them at all: bats feed mostly on
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moths, and less than 2% of their gut content is mosquitoes. "If you're
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expending energy," says medical entomologist Janet McAllister of the
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Centers for Disease Control and Prevention in Fort Collins, Colorado,
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"are you going to eat the 22-ounce filet-mignon moth or the 6-ounce
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hamburger mosquito?"
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With many options on the menu, it seems that most insect-eaters would
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not go hungry in a mosquito-free world. There is not enough evidence of
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ecosystem disruption here to give the eradicators pause for thought.
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## At your service
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As larvae, mosquitoes make up substantial biomass in aquatic ecosystems
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globally. They abound in bodies of water ranging from ephemeral ponds to
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tree holes[2](#B2) to old tyres, and the density of larvae on flooded
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plains can be so high that their writhing sends out ripples across the
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surface. They feed on decaying leaves, organic detritus and
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microorganisms. The question is whether, without mosquitoes, other
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filter feeders would step in. "Lots of organisms process detritus.
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Mosquitoes aren't the only ones involved or the most important," says
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Juliano. "If you pop one rivet out of an airplane's wing, it's unlikely
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that the plane will cease to fly."
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![Mosquito larvae form a substantial part of the biomass in water pools
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worldwide.](/news/2010/100721/images/_tmp_articling-import-20100721084308398938_466432a-i3.0.jpg)
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Mosquito larvae form a substantial part of the biomass in water pools
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worldwide.
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M. & P. FOGDEN/MINDEN PICTURES/FLPA
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The effects might depend on the body of water in question. Mosquito
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larvae are important members of the tight-knit communities in the
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25–100-millilitre pools inside pitcher plants[3](#B3),[4](#B4)
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(Sarracenia purpurea) on the east coast of North America. Species of
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mosquito (Wyeomyia smithii) and midge (Metriocnemus knabi) are the only
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insects that live there, along with microorganisms such as rotifers,
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bacteria and protozoa. When other insects drown in the water, the midges
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chew up their carcasses and the mosquito larvae feed on the waste
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products, making nutrients such as nitrogen available for the plant. In
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this case, eliminating mosquitoes might affect plant growth.
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In 1974, ecologist John Addicott, now at the University of Calgary in
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Alberta, Canada, published findings on the predator and prey structure
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within pitcher plants, noting more protozoan diversity in the presence
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of mosquito larvae[5](#B5). He proposed that as the larvae feed, they
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keep down the numbers of the dominant species of protozoa, letting
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others persist. The broader consequences for the plant are not known.
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A stronger argument for keeping mosquitoes might be found if they
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provide 'ecosystem services' — the benefits that humans derive from
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nature. Evolutionary ecologist Dina Fonseca at Rutgers University in New
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Brunswick, New Jersey, points as a comparison to the biting midges of
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the family Ceratopogonidae, sometimes known as no-see-ums. "People being
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bitten by no-see-ums or being infected through them with viruses,
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protozoa and filarial worms would love to eradicate them," she says. But
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because some ceratopogonids are pollinators of tropical crops such as
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cacao, "that would result in a world without chocolate".
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Without mosquitoes, thousands of plant species would lose a group of
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pollinators. Adults depend on nectar for energy (only females of some
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species need a meal of blood to get the proteins necessary to lay eggs).
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Yet McAllister says that their pollination isn't crucial for crops on
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which humans depend. "If there was a benefit to having them around, we
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would have found a way to exploit them," she says. "We haven't wanted
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anything from mosquitoes except for them to go away."
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Ultimately, there seem to be few things that mosquitoes do that other
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organisms can't do just as well — except perhaps for one. They are
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lethally efficient at sucking blood from one individual and mainlining
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it into another, providing an ideal route for the spread of pathogenic
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microbes.
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"The ecological effect of eliminating harmful mosquitoes is that you
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have more people. That's the consequence," says Strickman. Many lives
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would be saved; many more would no longer be sapped by disease.
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Countries freed of their high malaria burden, for example in sub-Saharan
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Africa, might recover the 1.3% of growth in gross domestic product that
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the World Health Organization estimates they are cost by the disease
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each year, potentially accelerating their development. There would be
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"less burden on the health system and hospitals, redirection of
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public-health expenditure for vector-borne diseases control to other
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priority health issues, less absenteeism from schools", says Jeffrey
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Hii, malaria scientist for the World Health Organization in Manila.
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Phil Lounibos, an ecologist at the Florida Medical Entomology Laboratory
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in Vero Beach says that "eliminating mosquitoes would temporarily
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relieve human suffering". His work suggests that efforts to eradicate
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one vector species would be futile, as its niche would quickly be filled
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by another. His team collected female yellow-fever mosquitoes (Aedes
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aegypti) from scrap yards in Florida, and found that some had been
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inseminated by Asian tiger mosquitoes (Aedes albopictus), which carry
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multiple human diseases. The insemination sterilizes the female
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yellow-fever mosquitoes — showing how one insect can overtake
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another.
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ADVERTISEMENT
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[![Advertisement](http://ad.doubleclick.net/ad/news@nature.com/;abr=!NN2;tile=1;ord=123456789?)](http://ad.doubleclick.net/jump/news@nature.com/;abr=!NN2;artid=article-one;pos=left;sz=300x250;ptile=2;ord=123456789?)
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Given the huge humanitarian and economic consequences of mosquito-spread
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disease, few scientists would suggest that the costs of an increased
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human population would outweigh the benefits of a healthier one. And the
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'collateral damage' felt elsewhere in ecosystems doesn't buy much
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sympathy either. The romantic notion of every creature having a vital
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place in nature may not be enough to plead the mosquito's case. It is
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the limitations of mosquito-killing methods, not the limitations of
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intent, that make a world without mosquitoes unlikely.
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And so, while humans inadvertently drive beneficial species, from tuna
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to corals, to the edge of extinction, their best efforts can't seriously
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threaten an insect with few redeeming features. "They don't occupy an
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unassailable niche in the environment," says entomologist Joe Conlon, of
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the American Mosquito Control Association in Jacksonville, Florida. "If
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we eradicated them tomorrow, the ecosystems where they are active will
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hiccup and then get on with life. Something better or worse would take
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over."
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Janet Fang is an intern in Nature's Washington DC office.
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- ## References
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1. Poulin, B., Lefebvre, G. & Paz, L.
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, 884-889
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(
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). | [Article](http://dx.doi.org/10.1111/j.1365-2664.2010.01821.x)
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2. Daugherty, M. P. & Juliano, S. A.
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Am. Midl. Nat.
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(
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