字幕表 動画を再生する 英語字幕をプリント Mosquitoes suck. And not just literally, their bites are also itchy and annoying, and certain species transmit parasites and viruses -- like the ones that cause Malaria, Yellow Fever, and Zika -- infecting and killing hundreds of thousands of people each year. And when we told you about the Zika virus a couple weeks ago, a lot of you had the same question: Why don’t we just kill them all? All of them! Kill all the mosquitoes! Humans are historically really good at making things go extinct. So it shouldn’t be too hard to get rid of these bloodsuckers… right? Yeah... not exactly. First of all, there are over 3,000 mosquito species worldwide, and only a couple hundred of them bite humans. Mosquitoes have been around for a lot longer than people, millions of years, and have survived lots of predators and environmental changes. So that would be a lot of tough insects to kill, and a lot of bug deaths that wouldn’t affect humans at all. And we’ve tried to eradicate mosquitoes before, mostly using chemicals that turned out to be awful for both the planet and us, like DDT. But let’s pretend that we were actually able to kill all the mosquitoes in some not-environmentally-apocalyptic way. Say, if I wished on a star, and the next day all mosquitoes just poofed out of existence. Would that be so bad for the Earth? Some scientists actually say no -- that if mosquitoes were suddenly ripped out of food webs, most ecosystems would heal pretty quickly, and other organisms would fill in those gaps. But other scientists argue that certain mosquito species do play important ecological roles. Take the mosquitoes that live in the Arctic of Canada and Russia. They fly around in gigantic thick swarms and make up a huge part of the biomass there. And these mosquitoes pollinate Arctic plants and are a major food source for migrating birds. Removing these guys -- or other, more southern species that are food for fish, birds, and other insects -- could send a ripple through ecosystems, endangering many other plants and animals. So we probably shouldn’t kill all the mosquitoes. But, we also don’t have to. We know which species are vectors, or carriers, of the worst viruses and parasites that can infect humans. So lots of researchers are currently targeting these species, and developing ways to kill them, or to kill the dangerous stuff inside them. Take the genus Aedes, which transmits lots of awful diseases. One particularly nasty species is Aedes aegypti, which is the primary vector for the Yellow Fever, Dengue, Chikungunya, and Zika viruses. A. aegypti is not just a pest, it’s one of the most medically significant pests. So it’s the focus of lots of recent experiments in targeted mosquito eradication. But some of the most promising research doesn’t set out to kill mosquitoes outright -- instead, it genetically modifies them. In 2015, a British company called Oxitec created male A. aegypti mosquitoes with a self-limiting gene, which basically means that the gene can stop their cells from functioning normally. When these genetically modified mosquitoes are released and mate with females in the wild, the self-limiting gene gets passed on to their offspring. Those offspring usually can’t develop properly and die before they become adults. No adult mosquitoes means no disease transmission. Likewise, a team of scientists in California inserted modified genes into a species of Anopheles mosquitoes, which are vectors for the parasite that causes Malaria. The modified genes cause the mosquitoes to kill the Malaria-causing parasites that live inside them, before they can transmit them to humans. And as a bonus, these parasite-destroying genes are designed to be passed on to 99.5% of the mosquitoes’ offspring. So, eventually, this entire species could be unable to transmit Malaria. And scientists think that this same technology could be applied to other mosquito species, and other parasites and viruses -- like Zika. Lastly, some scientists are fighting fire with fire -- or fighting viruses with bacteria -- by intentionally infecting A. aegypti mosquitoes with a bacterium called Wolbachia. Wolbachia seems to stop most viruses from growing inside these mosquitoes. So even if the mosquitoes bite people infected with, say, the Dengue virus, the virus wouldn’t survive inside the mosquito long enough to be transmitted to a new person. Now, because viruses mutate rapidly, scientists worry about accidentally creating deadly viruses that are resistant to Wolbachia. But a study released this week suggested a strategy to superinfect mosquitoes with more than one strain of the bacteria at a time. This way, the viruses can’t develop resistance to the bacteria as easily. And we can keep infecting mosquitoes, to keep them from infecting us. I mean, it’s only fair. So, basically, it would be incredibly difficult and possibly harmful to kill all the mosquitoes. But we may soon be able to focus on certain species and take away their ability to infect us, making the world a lot safer. But... not any less itchy. Thanks for watching this episode of SciShow News. Thank you to all of the people doing this amazing research. And thank you to our patrons on Patreon who support SciShow so it can always be freely available to everyone. If you want to help us keep making shows like this, you can go to patreon.com/scishow. And if you just want to keep getting smarter with us, you ca go to youtube.com/scishow and subscribe!