Why do some mosquitoes bite humans when others don’t? The answer might surprise you. The original story is from npr, here.
Listen to the recording and write no more than ONE word for each answer to questions 1 to 5
- How many different kinds of mosquitoes are there?
- Mosquitoes that bite humans spread what?
- Which word is used to describe the long-ago movement of mosquitoes to the Americas?
- Mosquito eggs won’t do what until they are wet?
- What is the main factor that decides whether a mosquito will bite a human or not?
Answers, transcript and clues below the image
- thousands
- viruses
- migrated
- hatch
- climate
Why One Dangerous Mosquito Developed A Taste For Human Blood
Well, here’s an all too familiar summertime sound.
(SOUNDBITE OF MOSQUITO BUZZING)
SHAPIRO: Ugh. Yeah, mosquitoes seem to love us – or at least our blood. NPR’s Nell Greenfieldboyce reports on why one important kind of mosquito developed a taste for humans.
NELL GREENFIELDBOYCE, BYLINE: There are thousands of mosquito species. And Lindy McBride says most of them will bite whatever animal happens to be around.
LINDY MCBRIDE: But there are these few species that really specialize in biting humans, so that’s unusual.
GREENFIELDBOYCE: McBride is a biologist at Princeton University who studies one of those human-targeting mosquitoes – Aedes aegypti. It spreads viruses like dengue and Zika, but it didn’t always seek out people.
MCBRIDE: African populations of the species Aedes aegypti didn’t really like humans. These were the ancestral – the original populations of the mosquito that, you know, were supposed to live in a forest and bite animals.
GREENFIELDBOYCE: She says sometime in the last five to ten thousand years, certain populations evolved to favor people and spread all around the world.
MCBRIDE: It looks like this mosquito migrated from West Africa into the Americas in the 1500s or 1600s, during the slave trade.
GREENFIELDBOYCE: Now, those are the mosquitoes that loved people. But in sub-Saharan Africa, there’s still groups of Aedes aegypti that aren’t all that thirsty for human blood. McBride and her colleague Noah Rose teamed up with collaborators in Africa to try to figure out why some mosquitoes liked people and others didn’t. The researchers collected mosquito eggs from forests, villages and cities big and small by putting out black cups that were lined with paper and filled with water. McBride says once eggs are laid in there, you can take them out on the paper and slowly dry them.
MCBRIDE: And then you can keep them on the shelf for months. You can stick them in your hand luggage and fly home with them. And they won’t hatch until you put them back in water.
GREENFIELDBOYCE: Back at the lab, they hatched them and tested the mosquitoes to see if they’d rather fly towards a human arm or a guinea pig. Now, McBride had thought forest mosquitoes would be really different from city ones.
MCBRIDE: But it turned out that human density had a surprisingly small effect.
GREENFIELDBOYCE: What did really matter was the climate.
MCBRIDE: When we collected mosquitoes in places with really long hot, dry seasons, they loved humans.
GREENFIELDBOYCE: Probably because in those regions, water is scarce – but humans tend to store it in pots and containers, so mosquitoes that hang around them have a better chance of surviving. The findings appear in the journal Current Biology.
Laura Duvall studies mosquitoes at Columbia University. She says, over the years, there’s been lots of speculation about why some prefer humans.
LAURA DUVALL: It could be that we’re slow compared to wild animals. It could be that our skin is easier to pierce.
GREENFIELDBOYCE: She finds this study and the link to water convincing. And what’s more, she says forecasting of disease outbreaks could be improved by taking into account all this diversity in how much this mosquito desires human blood.
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