I live in mosquito land.
Every monsoon evening, clouds of DDT swirl around the air sprayed diligently by the corporation workers to stem the mosquito population. Every store I go to has a new product being launched that guarantees a reduction in mosquitoes. Electric bats are used by the security folks in every apartment complex, to nuke the mosquitoes which bite them in their lonely sojourn at night.
It does not surprise me that one of the most popular queries received at Krya is a fervent demand for a natural mosquito repellent product. I get this from both consumers and retailers who are alarmed and appalled by the toxic load around their homes, especially of an insecticide nature.
And alarmed we should be.
DDT and DEET are the 2 primary chemical weapons of choice in our war against mosquitoes. DDT is used by city corporations in India, especially in Chennai as a mass fumigant to spray over large dense urban settlements and on stagnant urban water bodies with a hope to kill mosquitoes. It is not used inside homes or applied on the skin.
DEET is used inside homes in synthetic mosquito repellent products like coils and mats.
1. DDT ( Dangerous, Don’t Touch)
DDT is an insecticide, first synthesized in 1874 was used to control malaria and typhus during the Second World War, after its insecticidal properties were discovered by Pauly Mueller, the Swiss chemist who received a Nobel Prize for this work.
After the world war ended companies that manufactured DDT were forced to find a use for it in peacetime. DDT was re-purposed as an broad spectrum insecticide with two main applications
1) Agriculture and
2) Mosquito control.
DDT usage skyrocketed. Shortly however, scientists in the U.S started expressing concerns about the possible problems associated with the use of DDT.
In 1962, Rachael Carson’s seminal environmental book, “the Silent Spring”, which documented evidence against the indiscriminate use of pesticides, especially DDT, sounded the death knell for DDT
The overwhelming public reaction to the “Silent spring”, led to the beginning of the environmental movement and a widespread outcry which finally led to the U.S government banning the use of DDT in 1972. However, by this time the U.S had already used close to 1.3 million pounds of DDT.
Why are we talking about DDT today, if it was banned in the U.S in 1972?
This is because, DDT, like the recently debated Endosulfan, is a persistent organic pollutant (POP), which means its ill-effects last for decades after we stop using it.
More Shockingly, India is the only country that continues to manufacture DDT and is its largest consumer. China stopped manufacturing DDT in 2007.
Where does all the DDT go?
Indian made DDT is still used as an agricultural insecticide in many developing countries. DDT however does not degrade and from the fields finds its way to the lakes, rivers and oceans across the planet.
DDT sprayed on stagnant water bodies for mosquito control will eventually find its way to lakes and oceans.
Worse still, DDT used from the 1960’s before the US ban could still be present in the water bodies. This is why DDT is labelled as a persistent organic pollutant, it just refuses to leave.
DDT : From Water to Humans
When humans eat organisms exposed to DDT contaminated water, the pesticide accumulates inside the body and magnifies inside. As DDT absorption occurs best in the presence of fat, the largest and fattiest fish in the water bodies accumulate DDT which is then passed on the humans that eat them. Evidence for this transfer of DDT up the food chain was found when breast milk samples from countries that used DDT were found to contain DDT.
And it gets worse. Sustained consumption of DDT exposed food will cause storage or bio-accumulation of DDT in our bodies as it is very slow to metabolize and difficult to excrete.
DDT : Rise and Fall
When it was first introduced during World War 2, DDT seemed very effective against malaria causing vectors. However, within about 5 -10 years of continuous extensive usage, DDT resistant mosquito strains started to emerge. This was observed in Sri Lanka, Pakistan, Turkey, and Central America where DDT was then replaced with Malathion or Bendiocarb.
In India as well, DDT is mostly ineffective, due to its wide use in agricultural pest control, particularly in mango production.
Today, even WHO acknowledges the growing resistance to DDT, and maintains that DDT should be used only after ensuring that the mosquitoes do not have DDT resistance.
Apart from being an ineffective weapon against mosquitoes, the potential side effects of using DDT are numerous.
It is a potential carcinogen which bio accumulates in the liver and can cause liver cancer. DDT can also temporarily damage the nervous system. It could also reduce reproductive success.
To sum, DDT which is now known to be ineffective after extensive continuous usage, encourages the development of resistant super mosquitoes and is dangerous to human health, still continues to the official first line of defence sanctioned by the government.
If DDT is the large scale, area-wide mosquito control weapon, DEET is the key chemical ingredient of personal protection against mosquitoes inside our homes.
What’s eating DEET ?
DEET, developed by the U.S army, was originally tested as a pesticide on farms and entered civilian use in 1957.
DEET is the active chemical in mosquito lotions and mats across the world and works as a true repellent (unlike DDT which kills) as mosquitoes intensely dislike the smell of this chemical.
DEET is bad news for human health, potentially damaging to brain cells. DEET causes brain cell death and behavioural changes in rats after frequent and prolonged use. This exposure causes neurons to die in the regions of the brain that control muscle movement, learning, memory and concentration.
With heavy exposure to DEET, human may experience memory loss, headaches, weakness, fatigue, muscle and joint pain, tremors and shortness of breath. These symptoms may not be evident until months or even years after exposure.
Extensive large scale testing on the short term, occasional use and long term effects of DEET on humans is required before we can pass any judgement on its safety.
DEET is used extensively in mosquito repellent products in the U.S, especially in personal protection lotions, which can contain upto 100% DEET.
Active ingredients used in India
The extent of DEET usage in India is difficult to estimate as the same companies that declare ingredients in other countries (like the US) don’t not do so in India. In fact during research for this article it was very difficult to determine the key ingredients of mosquito repellents sold in India.
In India, mosquito coils are cheap and widely used, followed by mats. Mosquito skin lotions and sprays are also emerging on the scene.
Research papers on Mosquito coils proved to be the most fruitful source of information on ingredients. In India, coils use various active ingredients like pyrethrum, synthetic pyrethrins, allethrin, and others. They burn for upto 8 hours, and are cheap and easy to use.
However recent studies show that the smoke generated from coils has a lot of health concerns. Burning one mosquito coil produces the same amount of particulate mass similar to burning 75 – 137 cigarettes! The emission of formaldehyde from one burning coil can be as high as that released by 51 cigarettes!
Piperonyl butoxide, another common ingredient in coils, has been linked in a 2011 study to delayed mental development in young children (36 months) when their mothers were exposed to it during their third trimester of pregnancy. Children who were highly exposed scored 3.9 points lower on their mental development Index than others.
Synthetic pyrethroids like allethrin and resmethrin are used in repellent sprays and mats. While these compounds have low toxicity towards humans, they are highly toxic to fish and bees and also to cats. The true ecological impact of these chemicals is yet to emerge and we should be wary of their use.
To sum, the chemicals used in domestic mosquito repellents like DEET and pyrethroids pose an equal threat to human and ecological safety as DDT. So it appears that we are under attack inside our homes and when we step out by, mosquitoes & our current solutions seem to be worse than problem itself.
All about Mosquitoes
Over 3500 species of mosquitoes have been described from across the world. Those that bite humans as a matter of habit usually serve as vectors for diseases like malaria, dengue, chikungunya, etc.
Only the female of the species suck blood, and the protein in the blood is used by the female to create the material for new eggs. The rest of her meal comes from plant based nectar.
Like all insects, mosquitoes go through 4 stages in their development: egg, larva, pupa and adult. The eggs are often laid in water, although some species can even use moist mud or disused tires or other objects to lay their eggs.
Artificial water containers like tires, flowerpots, etc are used by some of the most dangerous mosquito species to lay their eggs like Aedes aegypti, which transmits dengue and yellow fever.
Most mosquito species are crepuscular, preferring to bite at dawn or dusk and seek cool, sheltered places to roost.
Mosquitoes cannot fly for prolonged periods; they need to rest frequently in-between hunts before they can fly again.
The female mosquito hunts her human blood host 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 in their sweat. Human beings have 3 different types of skin glands – sebaceous glands that produce oil to protect skin and hair (found all over the body and especially on your face and head); eccrine glands (found all over the body) that produce sweat to regulate temperature, and the apocrine glands found in the armpit and genital areas.
In human beings, the eccrine glands are the most abundant sweat glands, which set us apart from other mammals in the sheer volume of sweat we produce. The composition of our secretions also differs, as human skin oil is full of carboxylic acids, which draw mosquitoes to us.
This means that we humans are the perfect prey for mosquitoes and through our secretions we are irresistible to them.
The bacteria that live on each one of us is unique, – 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 what we eat and what we do.
The important chemicals that attract mosquitoes are a blend of ammonia, lactic acid, Octenol (secreted in sweat and breath), several carboxylic acids, acetone, and dimethyl disulfide, triglycerides from our skin and carbon dioxide from our breath.
Lactic acid, acetone and dimethyl disulfide seem to be the most potent lure in this set. Lactic acid is secreted after a workout, acetone is a by product of the body burning fat, and dimethyl disulfide is secreted when bacteria on the skin break down protein (result of oil and sebum secretion by the sebaceous glands).
A shower after a workout is therefore strongly indicated to make us less attractive to mosquitoes, with the gym clothes being stored away in a closed container or washed immediately.
What we eat also affects how irresistible we smell to mosquitoes. Drinking beer for example, can give our body odour a magnetic allure. Dimethyl disulfide, a favourite of the mosquitoes, is a popular food additive, in onion & , garlic flavours, cheese, meats, soups, savoury flavours, and fruit flavours – presumably consuming these foods would add to the dimethyl disulfide secretions from our body.
Sweaty socks can trap these chemicals for a long time, which also explains why you would find a lot more mosquitoes buzzing around unwashed laundry.
To sum up:
- Mosquitoes need a place to lay eggs, preferably damp or disused spots around the home.
- They hunt by smell and are attracted to odours released by perspiration.
- Specific odours they are attracted to are a result of high perspiration activities, unwashed laundry with the odours of sweat, unwashed hair and skin with accumulated sebum and sweat.
- Given their limited ability to fly for a long time, they need places to rest between hunts.
- They hunt at fixed times, seeking to enter homes around dawn or dusk.
Now that we are armed with the data that Sherlock Holmes so eloquently asked for, here are some of the practices we follow around our home to control mosquitoes from lording over us.
Controlling mosquitoes naturally and sustainably
Our first line of defence is the insect screen fixed to all windows which prevent mosquito entry.
We then audited our home to check for and damp / moist mud. The surface of the soil in our plants is covered with dry compostable material like dried leaves, and of course the dried compostable residue from the Krya detergent. This keeps soil dry and deters egg laying. Soapberries are also known to repel larval and pupal stage mosquitoes.
The next part of the home audit checked for clutter in the home, which provides the mosquitoes a pit stop in between their hunts. (remember their limited flight span). Our home is furnished in a minimalistic style. We also strive to put away clothes and other objects inside closed cupboards. This takes away their pitstops.
The home audit worked as bouncers to keep the mosquitoes away but gate crashers keep on coming in and still need to be tackled.
We mop our floors with a formulation of soapberry liquid and eucalyptus oil. Soapberries are insect repellents and of course clean really well, and Eucalyptus oil is a powerful mosquito repellent almost on par with DEET. Its strong fragrance naturally repels mosquitoes, especially when used around dusk, when the hunt begins. The sweet bonus of this natural formulation is the lovely spa-like aroma after the mopping is done.
We burn traditional Benzoin resin (Sambrani in Tamil) every evening around dusk. We infuse the benzoin resin smoke around the entire home .
Benzoin resin comes from the bark of an aromatic tree of the Styrax genus. Styrax resin has been used from ancient times in incense and in medicines in India, Middle east, Greece and Rome, and is said to have strong anti bacterial , insect repelling properties.
Benzoin resin appears to repel mosquitoes, and acts as a good cleansing ritual as well in the home. It is an acquired smell though and in high amounts can cause headaches, so start small and do not go overboard.
For more ideas on creating your own, great smelling insect repelling floor cleaner, do try out the formulation given in our downloadable guide here.
We bathe every evening and add a few drops of neem oil to the bath water. We do not use strong smelling synthetic soap, and stick to natural soaps which use essential oils instead of synthetic fragrances. Many synthetic fragrances especially those from the floral-fruity family use Octenol in their formulation which we now know to be a mosquito magnet. Regular shampoos could also be a source of Octenol and we only use a natural hair wash.
Deodrants are another rich source of octenals besides being hazardous to humans and environment. A alum stick which we blogged about earlier is a super alternative.
At the end of this epic post, living a mosquito free life is clearly an art and a science. There is no silver bullet in the story which will magically eliminate mosquitoes. The answer to all problems of urban life lie in understanding root causes and designing a sustainable life for ourselves.