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A hunter’s instincts

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Humans are the perfect prey for mosquitoes. PREETHI SUKUMARAN finds out why.

Chemical-based methods to control mosquitoes pose many dangers. The key to protecting ourselves without harming the environment lies in understanding the behaviour of these parasites.

Over 3,500 species of mosquitoes are there in the world, but only 150 of them cause harm to human beings and serve as vectors for diseases such as malaria, dengue and chikungunya. Female mosquitoes are the ones that suck blood, and the protein is used to create the material for new eggs. The rest of her meal comes from plant-based nectar. Like all insects, mosquitoes go through four developmental stages; egg, larva, pupa and adult. The eggs are often laid in water, although some species can even use moist mud or disused tyres or other objects.

Our first step in mosquito prevention is to therefore examine our home for ideal egg-laying spots such as artificial water containers (tyres or flowerpots), which are used by species such as Aedes aegypti , which transmits dengue and yellow fever to lay eggs. Most mosquito species are crepuscular, preferring to bite at dawn or dusk and seek cool, sheltered places to roost. So, do things like closing all doors and windows at dusk to prevent their entry.

Mosquitoes cannot fly for long; they need to rest frequently in between hunts before they can fly again. We should therefore pay special attention to identifying roosting spots. For example, a pile of folded clothes or a stack of books on the table are ideal roosting spots at night. The female mosquito hunts mainly through smell, by the unique combination of odour molecules in human sweat. Out of 72 odour receptors present in the antennae of the female mosquito, 27 are present to detect organic substances that emanate from human sweat.

Everyone perspires and produces a mixture of chemicals.

The composition of our secretions, our skin oil is full of carboxylic acids, attracts mosquitoes. This means that humans are the perfect prey. Furthermore, each of us has a unique set of bacteria living on our skin — this individual bacterial fingerprint goes to work to break down the molecules in sweat and cause an odour.

These differences explain why certain people are bigger mosquito magnets than others. This mosquito attractiveness can even change daily depending on our food and activities.

Of the several bodily secretions, lactic acid, acetone and dimethyl disulfide seem to be the most potent. Lactic acid is secreted after vigorous physical activity, acetone is a byproduct of the body burning fat, and dimethyl disulfide is secreted when bacteria on the skin break down protein.

Keeping ourselves clean and odour-free is an important line of defence. What we eat also affects how irresistible we smell to mosquitoes. Drinking beer, for example, can give our body odour a magnetic mosquito allure. Dimethyl disulfide, a favourite of the mosquitoes, is a popular food additive, in onion and garlic flavours, cheese, meats, soups, savoury flavours, and fruit flavours and might add to the dimethyl disulfide secretions of our body.

Sweaty clothes and socks can trap these odour-causing chemicals.

These clothes should be put away in a covered container or washed frequently to prevent forming an attractive spot for mosquitoes.

The composition of our secretions, which contains carboxylic acids, attracts mosquitoes

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