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Mosquito Smell Cycle

Mosquito Smell Cycle Anopheles gambiae mosquito
Photo Credit: James D. Gathany, CDC

Researchers have discovered that mosquitoes have a better sense of smell at night.


Transcript

Mosquitoes’ smell cycle. I’m Bob Hirshon and this is Science Update.

At nighttime, mosquitoes amp up their sense of smell by cranking out more odor-sensitive proteins. This according to biologists at the University of Notre Dame’s Eck Institute for Global Health, including Zain Syed, Giles Duffield, and Samuel Rund. Rund says they collected mosquito antennae every four hours, and compared the proteins they produced at different times.

Rund:
And we found that many of them, especially the OBPs, odorant-binding proteins, had levels higher at night, when the mosquito is flying around and host-seeking, than during the day, when they’re mostly just resting.

Syed says this probably lets the mosquitoes optimize their body’s resources. Other work suggests that artificial light may not only mute their sense of smell, but make them less interested in feeding. This could lead to a light-based strategy to control mosquito-borne diseases. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

For mosquitoes, a good sense of smell is essential to survival. Using their antennae, they can detect odors in the air from 100 feet away or more. These odors tell them where their next dinner might be. Both male and female mosquitoes feed on plant materials like nectar, but in many species, the females also feed on human and animal blood. For them, compounds found in sweat and exhaled breath, including carbon dioxide and and alcohol called octenol, are especially enticing.

Mosquitoes generally feed at dusk and dawn, and rest during midday. This study shows that when mosquitoes rest, their sense of smell takes a break as well. At night, mosquito antennae produce more odorant-binding proteins (ODPs), which help them to detect odors. During the days, production of ODPs drops.

The researchers discovered this by keeping a large number of captive mosquitoes, of the same type that transmit deadly malaria. At four-hour intervals, they removed some mosquitoes from the group, ground up their antennae, and measured the levels of odorant-binding proteins in them. 

It makes sense to think that mosquitoes smell better at night, when they're active. But looking at it the other way around, it's a little more mysterious: why would the mosquitoes' bodies go through the trouble of dropping ODP production during the day? Why not just keep up the nighttime levels, just in case an opportunity for a midday snack comes up?

The answer isn't known. But generally, in cases like this, scientists assume that the animal's body has evolved to conserve resources. Every substance an organism's body makes takes energy, nutrients, water, and other valuable resources. Making only what's needed, when it's needed, helps the animal use its energy budget most efficiently, just like turning off the lights at night when we're asleep saves electricity (and money). 

Mosquitoes not only become better smellers when the sun goes down; they also become much more active. In many parts of the world, mosquito bites aren't just a nuisance—they spread fatal diseases like malaria and dengue fever. So any way to make mosquitoes bite less could help protect human lives. 

Based on this research, it's possible that adding some kind of nighttime lighting to a home, tent, or place where people gather could decrease mosquito bites. Syed says it wouldn't necessarily have to be full lights all night long—it's possible that a burst of light at the right intervals could do the trick.

Now try and answer these questions:

  1. When are mosquitoes active? When do they bite? How does this relate to their sense of smell?
  2. How did the researchers determine when the mosquito's sense of smell becomes sharper and duller?
  3. Why is light an attractive potential mosquito repellent? What are some advantages and disadvantages that you can imagine?  

You may want to check out the September 27, 2013, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: Spider venom could be the next insecticide, debunking the myth of extracting dinosaur DNA from insects preserved in amber, and insect legs that bear an uncanny resemblance to modern machinery.

In the Science Update West Nile Weather, hear how scientists have found a way to predict the severity of a West Nile outbreak for the year.

Photojournalist Adam Nadel offers insights into his exhibition, Malaria: blood, sweat, and tears, which was featured in the AAAS Gallery in 2012.

Some plants can smell too. In the Science Update Plants Smell Danger, learn about a type of plant that can sense mating chemicals from fruit flies, and builds up its defenses when it does.


Going Further


For Educators

In the Science Update lesson West Nile Weather, hear how scientists have found a way to predict the severity of a West Nile outbreak for the year.

Photojournalist Adam Nadel offers insights into his exhibition, Malaria: blood, sweat, and tears, which was featured in the AAAS Gallery in 2012.

Some plants can smell too. In the Science Update lesson Plants Smell Danger, learn about a type of plant that can sense mating chemicals from fruit flies, and builds up its defenses when it does.


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