[ti:Why Do Mosquitoes Choose to Bite You]
[ar:Marsha James]
[al:Science In The News]
[by:www.21voa.com]
[00:00.00]Mosquitoes have an extraordinary ability to target humans 
[00:06.06]far away and fly straight to their unprotected skin. 
[00:11.54]Regrettably, mosquitoes can do more than cause an itchy wound. 
[00:18.13]Some mosquitoes spread several serious diseases, 
[00:22.87]including Dengue, yellow fever and malaria.
[00:27.56]Over one million people worldwide die from these mosquito-borne diseases each year. 
[00:36.44]New research now shows how mosquitos choose who to bite.
[00:43.77]Mosquitoes need blood to survive. 
[00:49.97]They are attracted to human skin and breath. 
[00:54.99]They smell the carbon dioxide gas -- which all mammals breathe out. 
[01:01.92]This gas is how mosquitoes know that a warm-blooded creature is nearby.
[01:09.04]But mosquitoes also use their eyes and sense of touch. 
[01:15.30]Michael Dickinson is a professor at the California Institute of Technology. 
[01:22.43]His research shows how these small insects, with even smaller brains, 
[01:29.47]use three senses to find a blood meal.
[01:33.86]"We suspected from research that we had been doing on fruit flies 
[01:38.19]that vision might play a very large and underappreciated role 
[01:42.74]in allowing the mosquito to really home in on the potential host target."
[01:48.59]Michael Dickinson's team used plumes ¨C material that rises into the air -- 
[01:56.60]of carbon dioxide gas into a wind tunnel. 
[02:01.08]They then used cameras to record the mosquitoes. 
[02:07.30]The insects followed the plume.
[02:10.87]Then, the scientists placed dark objects on the lighter colored floor and walls of the tunnel. 
[02:20.25]Mr. Dickinson said, at first, the mosquitoes showed no interest in the objects at all.
[02:29.06]"What was quite striking and quite surprising is 
[02:32.92]that the mosquitos fly back and forth for hours--these are hungry females--
[02:36.96]and they completely ignore the objects on the floor and wall of the tunnel. 
[02:41.42]But the moment that they get a hit of CO2, they change their behavior 
[02:45.85]quite dramatically and now would become attracted to these little visual blobs."
[02:51.10]This suggested to the researchers that a mosquito's sense of smell 
[02:57.42]is more important in the search for food. 
[03:01.31]Once mosquitoes catch a smell of a human or animal, they also follow visual cues.
[03:09.85]"This really makes a lot of sense because if the mosquitoes were distracted 
[03:13.66]by every visual object in their world, they would just waste all their time. 
[03:18.41]This case, they only start paying attention 
[03:21.17]when their nose tells them that there might be a host nearby."
[03:25.70]This process happens several times over the course of a mosquito's flight. 
[03:32.23]Michael Dickinson explains.
[03:35.07]"What some of the details of our experiments indicated 
[03:38.60]is that it's very hard to fool them over the long run. 
[03:41.93]They will always get their man or woman over time 
[03:45.00]because they'll just keep repeating this strategy until they find a yummy meal. "
[03:50.72]Matt DeGennaro is a scientist at Florida International University. 
[03:56.80]He says understanding a mosquito's way of finding its host 
[04:03.08]could help prevent those insects from biting. 
[04:06.71]He is working to create genetic changes that affect the mosquito's sense of smell.
[04:14.46]"We need to know which genes control this process at all these different stages. 
[04:19.41]And then we can use that knowledge to design a new perfume 
[04:24.71]that could block the mosquito's sensation of us or could trigger 
[04:29.83]certain receptors that signal danger to the mosquito and then cause them to stay away."
[04:36.88]The study, published in Current Biology, details the steps of the mosquito's flight 
[04:44.37]so that we may one day have a fighting chance against the biting insect.
[04:51.67]I'm Marsha James.
[04:54.45]¸ü¶àÌýÁ¦Çë·ÃÎÊ51voa.com