Of the more than 3,000 species of mosquitoes in the world, just a small number specialize in sucking human blood. How mosquitoes track us down so effectively isn’t currently known, but it matters, since they carry dangerous diseases which may cause death.
“In fact, stopping these annoying insects in their tracks could save up to half a million lives lost to those diseases each year,” said Carolyn Gauff, a professor of ecology and evolutionary biology at the Princeton Neuroscience Institute. That’s why Gauff’s team wanted to understand how they find and target humans.
Mosquitoes mostly choose what to bite based on odor (气味). Knowing how a potentially disease-carrying mosquito finds a person, while ignoring other warm-blooded animals, is a key question. But it’s not easy to answer, since any animal smell is made up of hundreds of chemicals mixed together in specific percentage. “The actual chemicals that are found in human odor are basically the same as the chemicals found in animal odor—it’s the percentages and the relative large amount of those substances in human mixtures that’s unique,” said Gauff.
To investigate, researchers decided to record neural activity in the brain of mosquitoes while exposing them to natural human and animal odor samples. They collected odor samples from about 40 different animals. When they compared some of those with the 16 human samples, something jumped out. Decanal is particularly rich in human skin. Common in the natural world, in humans, decanal comes from another, more complex substance. When one component of our skin’s natural oils, sapienic acid, breaks down, decanal is left over. This acid is only found in human beings. It’s what likely leads to the high levels of decanal that help the mosquitoes smell their way to us.
Understanding what the mosquitoes are targeting is only part of the story; knowing how they do it is also important. To see exactly how mosquitoes use this sense, scientists used genetically modified (转基因的) mosquitoes so that they could cut open mosquitoes’ heads and watch neurons firing when they’re exposed to human and animal odors. The research team already knew that mosquitoes have about 60 different types of neurons that sense odors, so when they looked in the insects’ brains, they thought they might see a lot of activities. But it was surprisingly quiet, meaning that the signal was perhaps quite simple, down to just a couple types of neurons. “One type of neuron responded really strongly to both humans and animals. Another type of neuron responded to both—but it responded much more strongly to humans than animals,” Gauff said.
How to keep mosquitoes’ decanal signal from being transmitted will be the research team’s next focus. Gauff hoped their current work could be used to make mosquito killers and attractants to prevent disease.
12. What’s the final purpose of the research conducted by Gauff’s team?
A.To study why only certain mosquitoes suck human blood. |
B.To investigate the neural activity in mosquitoes’ brains. |
C.To test the effectiveness of mosquito killers. |
D.To help prevent deadly diseases caused by mosquitoes. |
13. To which substance(s) would mosquitoes mostly be attracted?
A.Remains of decomposed sapienic acid. | B.Chemicals in the environment. |
C.Decanal generated in human blood. | D.Natural oil from human skin. |
14. What can we learn from the passage?
A.Chemicals found in human and animal odors are quite different. |
B.Genetically modified mosquitoes are not sensitive to human odor. |
C.Further research will focus on odor signal and neural connection. |
D.Most mosquito neurons are not involved in responding to human odor. |
15. From the last paragraph, which option accurately describes the future usage of Gauff and his team’s research?
A.Developing more effective mosquito killers. |
B.Studying of mosquito neural connections in response to odor signals. |
C.Analyzing the types of neurons in mosquitoes. |
D.Discussing the benefits for preventing mosquitoes from transmitting the decanal signal. |