Nature 466, 432-434, doi:10.1038/466432a
Eradicating any organism would have serious consequences for ecosystems- wouldn’t it? Not when it comes to mosquitoes,finds Janet Frang.
Every day, Jittawandee Murphy unlocaks a hot, padloacked room at the Walter Reed Army Institute of Research in Silver Spring, Maryland to a swarm of malaria carrying mosquitoes Anopheles stephensi. She gives million of larvae a diet of ground up fish food, and offers the gravid females blood to suck from the bellies of unconscious mice they drain 24 of the rodents a month. Murphy has been studying mosquitoes for 20 years, working on ways to limit the spread of the parasites they carry. Still, she says she would rather they were wiped off the Earth.
That sentiments is widely shared. Malaria infects some 247 million people worldwide each year, and kills nearly one million. Mosquitoes cause a huge further medical and financial burden by spreading yellow fever, dengue fever, Japaneses encephalitis, Rift Valley fever, Chikunjunya virus and West Nile virus. the there’s the pest factor: they form swarms thick enough to asphyxiate caribous in Alaska and now, as their numbers reach a seasonal peack, their probosises are plunged into human flesh across the Northern Hemisphere.
So what would happen if there were none? Would anyone or anything miss them? This question is asked to scientists who explore aspects of mosquito biology and ecology and unearthed some surprising answers.
There are 3,500 named species of mosquito of which only a couple of hundred bite or bother humans. They live on almost every continent and habitat, and serve important functions in numerous ecosystems. “Mosquitoes have been on Earth for more than 100 million years,” says Murphy, “ and they have co-evolved with so many species along the way.” Wiping out a species of mosquitoes could leave a predator without prey, or a plant without pollinator. And exploring a world without mosquitoes is more than an exercise in imagination: intense efforts are under way to develop methods that might rid the world of the most pernicious, disease carrying species.
Yet in many cases, scientists acknowledge that the ecological scar left by a missing mosquito would heal quickly as the niche was filled by other organisms. Life would continue as before or even better. When it comes to the major disease vectors, “it’s difficult to see what the downside would be to removal, except for collateral damage,” says insect ecologist Steven Juliano, of Illinois State University in Normal. A world without mosquitoes would be “more secure for us”, says medical entomologist Carlos Brisola Marcondes from the Federal University of Santa Catarina in Brazil. “The elimination of Anopheles would be very significant for mankind.”
Arctic Pests:Elimination of mosquitoes might make the biggest ecological difference in the Arctic tundra, home to mosquito species including Aedes impiger and Aedes nigripes. Eggs laid by the insects hatch the next year after snow melts, and development to adults takes only 3-4 weeks. From northern Canada to Russia, there is a brief period in which they are extraordinarily abundant, in some areas forming thick clouds. “That’s an exceptionally rare situation worldwide,” says entomologist Daniel Strickman, programme leader for medical and urban entomology at the US Department of Agriculture in Beltsville, Maryland. “There is no other place in the world where they are that much biomass.”
Views differ on what would happen if that biomass vanished. Bruce Harrison, an entomologist at the North Carolina Department of Environment and Natural Resources in Winston Salem estimates that the number of migratory birds that nest in the tundra could drop by more than 50% without mosquitoes to eat.Other researchers disagree. Cathy Curby, a wildlife biologist at the US Fish and Wildlife Services in Fairbands, Alaska, says that Arctic mosquitoes don’t show up in bird stomach samples in high numbers, and that midges are a more important source of food. “Wee as humans may overestimate the number of mosquitoes in the Arctic because they are selectively attracted to us,” She says.
Mosquitoes consume up to 300 milliliters of blood a day from each animal in a caribou heard, which are thought to select paths facing into the wind to escape the swarm. A small change in path can have major consequences in an Arctic valley through which thousands of caribou migrate, trampling the ground, eating lichens, transporting nutrients, feeding wolves and generally altering the ecology. Taken all together,then, mosquitoes would be missed in the Arctic but is the same true elsewhere?
food on the wing:”Mosquitoes are delectable things to eat and they’re easy to catch,” says aquatic entomologist Richard Merritt, at Michigan State University in East Lansing. In the absence of their larvae, hundreds of species of fish would have to change their diet to survive. “This may sound simple, but traits such as feeding behaviour are deeply imprinted, genetically, in those fish,” says Harrison. The mosquito fish Gambusia affinis for example is a specialized predator so effective at killing mosquitoes that it is stocked in rice fields and swimming pools as pest control that could go extinct. And the loss of these or other fish could have major effects up and down the food chain.
Many species of insect, spider, salamander, lizard and frog would also lose a primary food source. In one study published last month, researchers tracked insect eating house martins at a park in Camargue,France, after the area was sprayed with a microbial mosquito control agent. They found that the birds produced on average two chicks per nest after spraying, compared with three for birds at control sites.
Most mosquito eating birds would probably switch to other insects that, post mosquitoes, might emerge in large numbers to take their place. Other insectivores might not miss them at all: bats feed mostly on moths, and less than 2% of their gut content is mosquitoes. “If you’re expending energy,” says medical entomologist Janet McAllister of the Centers for Disease Control and Prevention in Fort Collins, Colorado,” are you going to eat the
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