Ecology: A world without mosquitoes
- Fang, Janet
Eradicating any organism would have serious consequences for ecosystems — wouldn't it? Not when it comes to mosquitoes, finds Janet Fang.
War against the winged
Humans have made many concerted, if not always effective, efforts to eliminate mosquitoes. The more successful attempts include the eradication campaign against Aedes aegypti in the early 1900s, which relieved yellow fever enough to allow the completion of the Panama Canal; and the use of the larvicide Paris Green to rid Brazil of the malaria vector Anopheles gambiae by 1940. Application of the adulticide DDT allowed the United States to be declared free of malaria in 1949.
But the chemicals sprayed then are banned in many countries now. “We can't mount those top-down, military-style efforts today,” says Roger Nasci, an entomologist at the Centers for Disease Control and Prevention in Fort Collins, Colorado. “And we don't have DDT any more. It came with a lot of baggage but was an outstanding product for mosquito reduction.”
Mosquito control using less-toxic chemicals is key to keeping the insects in Florida and parts of southeast Asia and Latin America at tolerable levels. Worldwide malaria control in 2010 requires about US$1,880 million for indoor residual spraying and $2,090 million for insecticidal nets.
“It's a complicated business, and that's why we still have mosquitoes,” Nasci says. “They're not going anywhere.”
Researchers are developing alternative mosquito-control methods; some are outlined below.
RNA interference
RNA-based insecticides kill female A. aegypti by promoting cell suicide[6]. “It basically tells the mosquito to go kill itself,” says Stanton Cope, director of the US Armed Forces Pest Management Board, Washington DC.
Formulation not yet developed to spray it in large quantities.
Male sterilization
Introduced in large-enough numbers, sterile males can slow reproduction. Screw worms were eradicated in the United States in the early 1980s in this way: irradiated pupae grew into sterile males that were released until the species bred itself out of existence.
Hasn't been widely field tested for mosquitoes.
Improved chemicals
Mosquitoes are becoming resistant to current adulticides, which target the nervous system. Researchers are seeking agents with new mechanisms, including natural products such as cedar oil.
Basic research to be done to find compounds and modes of action.
Mosquito traps
In 2003, Aedes taeniorhynchus was mostly eliminated from an island in Florida by researchers at the US Department of Agriculture, using traps that generate carbon dioxide to lure mosquitoes.
Good for gardens or small islands, but probably not feasible on a larger scale.