Mosquitoes transmit West Nile virus and other life-threatening diseases such as malaria. Female mosquitoes spread disease by first extracting blood from an infected animal or human and then biting an uninfected individual. Mosquitoes find us by smell. They have antennae-like receptors near their mouth parts that detect odors. Researchers have found new substances that may inhibit or block these odor receptors on mosquitoes better than current mosquito repellents and devices.
How mosquitoes find us
The odor receptors on mosquitoes can detect carbon dioxide in our breath even at a distance and upwind. When mosquitoes find us, other odors emanating from our body direct them to various parts of our skin.
Current mosquito controls
Mosquito controls include:
1. Mosquito nets
Mosquito nets work, but are not practical in many situations.
2. Mosquito magnets
The mosquito magnet is effective, because it uses a carbon dioxide source to attract mosquitoes. When the mosquitoes get close to the magnet, they are pulled in and die of dehydration. This device is expensive.
3. Electrical zappers
Electrical zappers attract many insects via UV light and kill them. But mosquitoes are not attracted to them.
4. Chemical repellents
The chemical DEET is part of many insect sprays. It is effective, but has to be reapplied. Some people report adverse effects.
5. Botanical repellents
Essential oils of plants such as citronella oil make strong mosquito repellants. Researchers at Iowa State University found that an extract of catnip was 10 times more effective than DEET. However, the active ingredients in many natural repellants are very volatile and need to be reapplied or replenished often.
Blocking mosquito odor receptors
Researchers at the University of California worked with three species of mosquitoes known to spread malaria, West Nile virus, dengue and yellow fever. The researchers found substances that inhibited or blocked the odor receptors on the mosquitoes so that they could not respond to carbon dioxide. The three types of substances were:
Substances, such as hexanol and butanol, were strong inhibitors of the carbon dioxide receptor on mosquitoes.
Odor chemicals, such as 2,3-butanedione, super-activated the carbon dioxide receptor, causing the receptor to become temporarily unresponsive to carbon dioxide.
Substances, such as 2-butanone, mimic carbon dioxide and attract mosquitoes to 2-butanone and not to the carbon-dioxide-laden breath of people. Such substances could be made into inexpensive traps to draw mosquitoes away from people.
Together with Kenyan colleagues, the researchers tested the newly discovered substances in a greenhouse in Kenya. They used two huts, outfitted with carbon dioxide traps to attract mosquitoes, but one hut also had a container with a mix of the inactivating substances. Hardly any mosquitoes entered the hut containing the carbon dioxide blocking substances compared to the hut only containing the carbon dioxide trap. The newly discovered substances work at very low concentrations and may lead to the development of more powerful mosquito repellants and traps.
Turner, S.L. et al. Ultra-prolonged activation of CO2-sensing neurons disorients mosquitoes. Nature (2011) 474: 87