Guests at the Cypress Cove Nudist Resort in Florida routinely emerge from the swimming pool and walk over to a nearby row of citrosa plants. They proceed to shake the shrubbery and then rub their hands on their thighs. No, this is not some sort of bizarre nudist ritual, it is just preparation for a spell of bite-free frolicking in the sun. The citrosa plants produce two compounds, citronella and citral, which are claimed to have mosquito repellent properties!
Have the nudists found a solution to a problem that has plagued mankind since times immemorial? If so, it would mean a lot more than peaceful barbecues and slap-free camping trips. It would mean the saving of lives!
Mosquitoes hold the unenviable record as the creature responsible for killing the most humans throughout our history. They have dispatched millions with malaria, yellow fever and encephalitis. Of course, the mosquito is not a conscious murderer; when it sinks its proboscis into our flesh, it is only trying to survive. Actually, the male is a vegetarian, it is only the female of the species that torments us. She bites, searching for a source of protein needed to nurture her eggs. Unfortunately, our blood is an ideal source of nutrients for this purpose.
As the female mosquito sucks blood, she injects a mix of chemicals to keep the blood from clotting. It is this mosquito saliva that can trigger the localized release of histamine, which in turn causes an allergic reaction and the associated itch. Far worse, disease-causing organisms which the prospective mother may have picked up from a previous meal may now be transferred to the new victim.
A great deal of research has been carried out to try and determine what makes a mosquito bite a certain individual. It is well known that some people are more attractive to the insect than others. Actually, if given the choice, many varieties of mosquitoes prefer animals.
Scientific evidence suggests that the mosquito selects its prey by sensing moisture, warmth, carbon dioxide and various bodily fragrances. Lactic acid, a product of muscle metabolism is a definite attractant. So is octenol, which is produced when plant material is digested. The breath of cows makes mosquitoes drool. They also find vegetarians particularly appealing. Mosquito traps that release carbon dioxide and octenol have already been used to significantly cut down on insect populations in the Florida Everglades.
Mosquitoes are also attracted by certain fatty acids produced by bacteria found on the skin. Since people have different microflora, they may indeed attract mosquitoes to different extents. Even certain parts of our anatomy may be more tempting to mosquitoes than others. Some species apparently prefer the fragrance of feet, others are drawn to more intimate areas. This of course may explain the nudists' habit of anointing their thighs with the citrosa scent.
So we are back to the citrosa. Promoters claim that the chemicals released by the plant block the mosquitoes' olfactory receptors and prevent them from zeroing in on their target. But scientific research, unfortunately, does not fully support this claim. When researchers thrust their hands into boxes filled with hungry mosquitoes, they find that citronella affords only minimal protection.
Consumers who rely on citronella-based bath oils, such as Avon's Skin-So-Soft, are buying into a myth. The amount of citronella it contains is not enough to repel mosquitoes. Neither is there a significant amount of coumarin, another plant-derived fragrance, which in high doses can act as a deterrent. Even the citronella candles that so many people rely on for backyard comfort owe their effectiveness more to the smoke they produce than the amount of citronella they disperse into the air.
Smoke really does keep the bugs away. But sound does not. The ultrasonic repellers on the market supposedly frighten insects away by mimicking the sound of the mosquito's greatest enemy, the bat. The Environmental Protection Agency in the U.S. concluded after extensive testing that none of the ultrasonic devices are effective.
There is one way that sound could, at least in theory, be put to a use. The characteristic buzzing of the mosquito is of course caused by the beating of its wings. When the female is desirous of mating, she produces a specific hum that brings the mate aflying. Indeed, a tuning fork struck at the right frequency will attract males. This idea could be used to trap the males and reduce the number of eggs laid. But of course, it would not prevent the females from biting.
So what does? The bugs can be attracted to blue light and zapped with electricity. This may make a dent in the population but some researchers suggest that the process can disperse microbes the insects may be carrying into the air. Not an attractive scenario. Better stick to chemistry.
Since the 1950s we have been relying on N,N-diethyl-meta-toluamide, mercifully abbreviated as DEET. This synthetic chemical does indeed bind to the mosquito's olfactory receptors and when properly used can keep the insects away for hours. The repellant effect is proportional to the concentration of DEET in a product. Unfortunately, so are the possible problems.
DEET can be absorbed through the skin; about 15% of a dose eventually shows up in the urine. In addition to allergic reactions, there have been rare reports of neurological problems including seizures and confusion. The risks can be minimized by not using products that contain over 35-40% DEET for adults and 10-20% for children. DEET also has an unpleasant odour and can damage some fabrics as well as plastics lenses in glasses. Still, millions of people use DEET regularly every year without significant problems. But a safer alternative is certainly desirable. And one may have been found.
Bite Blocker is a new entry in the mosquito repellent sweepstakes. The active ingredient, 2% soybean oil, is certainly innocuous. When mixed in a base of coconut oil, water, glycerin, lecithin, geranium oil and vanilla it protects as well as 20% DEET, and for a longer time. A single application can repel mosquitoes for ten hours!
There are various other folkloric repellants that people swear by although they have not been scientifically validated. Supposedly B vitamins block taste receptors that mosquitoes use when they search for blood. Advocates claim that taking yeast tablets raises the blood levels of vitamin B to an extent that affords protection. The mosquitoes may probe, but they will not bite.
Garlic also has a reputation as a deterrent to the sanguineous predator. But garlic loading hardly constitutes a convenient way of dealing with the problem. Neither does sleeping with pigs. According to some accounts, Mediterranean peasants capitalize on the mosquito's preference for pork over humans and allow their hogs to roam freely through the bedroom.
None of these remedies works for everyone. Not even DEET. Sometimes there is nothing left but bloodthirsty revenge. All you have to do is wait until the mosquito bites and then suddenly stretch the skin around the bite. This will trap the insect's proboscis and apparently cause the insect to keep sucking until it pops. One wonders what inquisitive mind discovered this phenomenon.
Maybe the same one that found that mosquitoes hate the scent of Bounce, the little sheet impregnated with fabric softener that we usually toss in the dryer. It seems that tying a sheet through a belt loop keeps the bugs away. Sounds great! But of course, having no belt loops, this does present a problem for nudists. I guess they will just have to keep shaking those citrosa plants. Or put on the DEET or the Bite Blocker.
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