September 25, 2006

Mosquito larvae destruction

The resonant frequency idea is apparently more than half-baked.
At least one company, New Mountain Innovations, claims to be able to destroy mosquito larvae up to a five foot radius by sending audio signals at the resonant frequency of the mosquito larvae air bladder. Go Michael! The story is good - now does it really work?

The concept is simple: Use acoustic energy to kill mosquito larvae before they can become biting adults. All mosquito larvae, regardless of species, have internal air bladders that help them breathe and move up and down in the water where they feed and grow. Send sound waves through the water and those bladders start to vibrate like a tuning fork. Eventually the bladder tissue ruptures, killing the larvae.
There is at least one scientific paper on this giving 1 MHz as the frequency of choice.

I'm still hopeful on getting adult mosquitoes in mid-flight. Suppose you were able to send back ultrasound at the frequency the mosquitoes are flapping their tiny wings. Could you (a) cause them to fall to the ground via destructive interference, or (b) cause their wings to rip off via constructive interference? That would a cool demo. The device would need to listen and then replay using large volume the correct frequency. Of course, since you could hear mosquitoes buzzing, perhaps this may not be such a good idea. The frequency here is 250-1000 Hz. Here's some more serious analysis.

Posted by torque at 1:49 AM | Comments (0) | TrackBack

Ultrasonic mosquito repellent - will it work?

I was wondering about this all night after a friend of ours mentioned it. Their grandkids are currently in Central Asia getting eaten alive by these little buggers. The question at hand is whether there is anything that technology can offer besides air conditioning, netting and hazardous chemicals. Enter the ultrasonic mosquito repellant. The original theory goes like this - bats, el mosquito's #1 enemy, emit sonar in the 20-50 kHz range. By mimicing these bats, the mosquitoes should take a hike. But does it work? Cecil Adam's straight dope concluded in 1977 "no" based on EPA testing in Chesapeake Bay. The Federal Trade Commission (FTC) and the Center for Disease Control in 2002 said "no" -- this time to a new set of frequencies set to mimic "male mosquitoes and dragonflies".

...ultrasonic products are not effective at preventing mosquito bites. It advises people to:
  • use insect repellent containing DEET, according to the manufacturer's instructions;
  • wear long-sleeved shirts and long pants;
    spread mosquito netting over infant carriers; and
  • stay indoors at dawn and dusk.
As of 2005, the verdict from the CDC was still a resounding "no" -- ""ultrasonic" devices are NOT effective in preventing mosquito bites."

But it is 2006 now. And these things still sell. Perhaps the theory has changed?

I doubt it. For a first hand account, check out Joe Kissell's blog on the topic. Don't think "it can't hurt". The Biting Insect Management Bulletin reports on Dr. Richard Gorham, of the Arctic Health Research Laboratory in Fairbanks.

Dr. Richard Gorham, of the Arctic Health Research Laboratory in Fairbanks, took an ultrasonic mosquito repeller to Sagwon on the North Slope. The machine emitted a kind of extremely high-pitched whine that supposedly sent mosquitoes far, far away. Gorham challenged that claim by testing the whiner at the height of mosquito season. A true scientist, he calibrated the mosquito density by exposing the back of his unprotected hand for five minutes, counting the number of mosquitoes that drew blood.

From that part of the experiment alone, Gorham was able to calculate that had he been stripped naked and tied to a post at Sagwon, he would have died from loss of blood in two and a half hours. Then he turned on the whining device, and found that with its help, he'd die more quickly. The number of mosquitoes biting within five minutes actually increased slightly. He was not surprised, since mosquitoes use their own characteristic whine as a method for finding mates; high-pitched whines can be the mosquito equivalent of a wolf whistle. The non biting male mosquitoes are most likely to be attracted, but females may also use such signals to detect happy clouds of their sisters zeroing in on food.

So, buyer really beware. To get more answers to more questions about mosquitoes, check out the Colorado State West Nile Virus FAQ. It is excessively thorough. The bottom line is that you are mostly stuck with N,N-diethyl-m-toluamide or N,N-diethly-3-methylbenamide (DEET) based solutions. Tough choice, long-term chemical poisoning or short-term death via encephalitis or West Nile?

We've established that the current set of ultrasonic devices are most likely not going to work. But perhaps this is a problem with the theory. Scaring the buggers away with the mutterings of bats, dragonfiles and male mosquitoes may not work, but consider the following: what if we design an ultrasonic mosquito repellent tuned to the resonant frequency of the mosquitoes brain... I wonder if we could cause the mosquitoes to explode in mid-flight...

Posted by torque at 12:59 AM | Comments (0) | TrackBack