It would be hard to find an insect more despised these days than the mosquito. The blood-sucking pest is considered more lethal to humans than any other animal in the world. It has long been blamed for spreading malaria that kills a half-million people each year and is now the villain behind the Zika virus that has sparked panic across South and Central America.
With little to no apparent value and the dangers of Zika to newborns becoming increasingly apparent, there are growing calls to wipe out mosquitoes. The web is filled with stories with headlines like "Let's Kill All the Mosquitoes" or "Would it be so bad if we killed all the mosquitoes?"
But exterminating an insect with upwards of 3,500 named species and that is ubiquitous across the globe would be no easy task. Most experts said it would be too costly and impractical and that it would take a heavy and unpredictable toll on the environment — harking back to the days of Rachel Carson's Silent Spring when excessive use of insecticides like DDT polluted waterways and killed off wildlife.
"I don't think it's realistic because there is going to be no silver bullet that is going to eradicate them all," said Joseph M. Conlon, the technical Advisor American Mosquito Control Association and an entomologist with the Navy for 20 years.
"I think, in trying to eradicate mosquitoes, we would probably cause too much environmental damage, collateral damage in doing it," he continued. "I'm not saying that if we eradicated mosquitoes their predators would all die off because there is no predator on the planet that has mosquitoes as their sole or even primary food source. But there is going to be some environmental damage and possibly in ways we couldn't even predict."
'Eliminating mosquitoes could leave predators without prey.'
Rich Merritt, an emeritus professor at Michigan State University who has worked with mosquitos for 25 years, agreed, but for very different reasons. He contends eliminating mosquitoes would deprive many fish, birds, and reptiles of a food source and even deny some plants a critical pollinator.
"These are not an organism that you should eliminate without repercussion of eliminating a major prey base for aquatic habitats – ponds, marshes, tree holes," Merritt said, noting that there are some fish that feed exclusively on mosquito larvae, spiders that catch adults in their webs, and bats that gobble up swarms of mosquitoes at night.
"They are a major food item especially in the tropics," he added. "My feeling is that they do play an important role in the ecosystem and also, the way they feed, they are filter feeders. In other words, they have a set of mouth parts like mini brushes and gather in particulates. In some habitats, they keep the water clean."
Even University of California Riverside's Omar S. Akbari, who has described mosquitoes as perhaps the most dangerous animals in the world, said extermination goes too far.
"I believe that exterminating all mosquitoes could have severe ecological consequences, as mosquitoes make up a substantial biomass in aquatic ecosystems globally," he said. "Eliminating mosquitoes could leave predators without prey."
Rather, Akbari, Conlon, and others called for a more "targeted approach" that focuses on mosquito species like Aedes aegypti and Aedes albopictus that are responsible for spreading dengue, chikungunya, and Zika, as well as yellow fever viruses, and 40 of the nearly 430 species from the genus Anopheles blamed for transmitting malaria.
"A small minority of the species play a serious role in transmitting the pathogens that cause diseases in humans, so it makes perfect sense from a public health standpoint to devise ways to keep those mosquitoes from biting people," said Dan Strickman, a senior program officer at the Bill & Melinda Gates Foundation. "We believe that we can be smart about mosquito control by targeting those locations where the disease problems occur and by using surveillance to tell us where we need to do a better job. Efficient mosquito control to reduce the way that malaria gets from person to person combined with curing people who carry the malaria parasites will create a malaria-free world without consigning any species to history."
Support for this approach has gained traction of late, partly due to the success of several innovative control methods. A British company, Oxitec, has developed genetically modified mosquitoes — making changes in the DNA of males that leaves them sterile and results in their offspring never reaching adulthood. Field trials in several locations including Malaysia and Brazil found the GMO mosquitoes reduced the location population of Aedes aegypti by 90 percent.
And this week in the journal PLOS Pathogens, a team of scientists reported on another control method that holds promise — using Wolbachia, a bacterium that naturally infects many insect species but not Aedes aegypti. By introducing the bacterium into the Aedes aegypti population, it protects the mosquito from contracting dengue, Zika, and other viruses and thus from spreading it onto their unsuspecting human host.
"With the rapid knowledge of mosquito biology, and physiology, and the development of new genetic tools, namely 'gene drives,' it may be possible to one day eliminate selected species of mosquitoes," Akbari said. "Given that only 100 or so of the 3,500 estimated mosquito species on earth bite humans, and of those, only around 50 vector human diseases, in the future, I believe it may be possible to target and eradicate just those selected vector species and leave the remaining non-vector species populations intact."
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