Geneticists get closer to knowing how mosquitoes sniff out our sweat | Science News for Students

Geneticists get closer to knowing how mosquitoes sniff out our sweat

A protein in the antennae of at least one species detects lactic acid coming off human skin
May 21, 2019 — 6:45 am EST
a macro photo of an Aedes aegypti mosquito

Geneticists have figured out one protein that an Aedes aegypti mosquito (shown) needs to sniff out the lactic acid in human sweat.

Alex Wild

Geneticists have found a scent-sniffer protein in the antennae of a mosquito. The protein is called IR8a. If that protein could be jammed, it might leave a bloodsucker confused about whether we’re human enough to bite.

Aedes aegypti is one of many mosquito species. It prefers human blood to that of other animals. The bad news: This mosquito can spread Zika and dengue. Those are two dangerous diseases.

Our skin and the many types of microbes that live on the outside of us shed lots of lactic acid. That acid makes up an unusually big part of the human scent, notes Matthew DeGennaro. He’s a geneticist who works at Florida International University in Miami.

Since the 1960s, researchers have mused that lactic acid might be one clue that Aedes aegypti uses to pick out humans. His team’s tests now show that these mosquitoes need IR8a to smell lactic acid.

The researchers worked with Aedes aegypti that make the proper IR8a. They also worked with some of these mosquitoes that make an altered form of IR8a. It doesn’t work properly. All of the insects were offered an alluring human arm or sweat-stained sleeve. Mosquitoes with the altered IR8a were only about half as likely to land on the skin or sweaty fabric as the normal insects. DeGennaro and his colleagues shared their findings March 27 in Current Biology.

The insect system for detecting odors is “very complex,” DeGennaro says. Mosquitoes rely on three families of odor-sniffing proteins. These proteins have overlapping abilities to identify chemicals in the air.

IR8a is a protein that targets acids, among other compounds. As a mosquito hunts, it mixes cues about floating chemicals with other information. These include heat, moisture and the sight of something biteable. A bloodsucker also notices the carbon dioxide we exhale. DeGennaro calls that “mosquito coffee.” It revs the insects up to get to work seeking a meal.

Power Words

(more about Power Words)

Aedes aegypti     A species of mosquito that can transmit the viruses responsible for several tropical diseases, including dengue fever, yellow fever and West Nile disease.

biology     The study of living things. The scientists who study them are known as biologists.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon dioxide     (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

colleague     Someone who works with another; a co-worker or team member.

component     Something that is part of something else (such as pieces that go on an electronic circuit board or ingredients that go into a cookie recipe).

compound     (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.

dengue     A potentially lethal infectious disease transmitted by mosquitoes. No vaccine yet exists to prevent infection with the virus responsible for the disease, which causes high fevers, severe headache, joint pain, pain behind the eyes, rash, bone pain and sometimes mild bleeding. A more severe form of the disease, known as dengue hemorrhagic fever can cause uncontrolled bleeding if not treated right away.

information     (as opposed to data) Facts provided or trends learned about something or someone, often as a result of studying data.

insect     A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

lactic acid     A chemical compound commonly found in milk and in exercising muscles.

microbiome     The scientific term for the entirety of the microorganisms — bacteria, viruses, fungi and more — that take up permanent residence on or within the body of a human or other animal.

moisture     Small amounts of water present in the air, as vapor. It can also be present as a liquid, such as water droplets condensed on the inside of a window, or dampness present in clothing or soil.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

vertebrate     The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.

Zika     A viral disease that can be transmitted to humans via mosquitoes. About 20 percent of infected people get sick. Symptoms include a slight fever, rash and pinkeye and usually fade quickly. A growing body of evidence suggests that the virus could also cause a devastating birth defect — microcephaly.

Citation

Journal:​ J.I. Raji et al. Aedes aegypti mosquitoes detect acidic volatiles found in human odor using the IR8a pathway. Current Biology. Published online March 28, 2019