Judging by the countless ads in the newspapers, ultrasonic pest repellers and electric bug killers are an unqualified success. People are buying them by the millions.
The only problem is that they don`t work to everybody`s satisfaction, including the government`s. Cockroaches and rodents ignore them, and they may even make your mosquito problem worse.
If the device is an electric zapper, it gives off an ultraviolet light that moths, June bugs and other night-flying insects find irresistibly attractive. When they attempt to reach the light bulb, a charged grill electrocutes them, emitting a hugely satisfying zap as the bugs hit the electric grid and are vaporized. Almost 10 million of these devices have been sold since 1980.
People run into trouble, though, when they place the machines in their back yards to knock off mosquitoes. Killing bugs is one thing; controlling pests is quite another. The electrocuters slaughter hordes of moths and other light-responding insects, but most of them don`t bite.
Mosquitoes, the main back yard pest of a balmy evening, also like the light, and more are drawn into the yard at night by the devices than would fly in on their own. But if, on their way to the light, mosquitoes sense people, they quickly change direction.
In the two controlled experiments to date, the devices did nothing at all to decrease the number of mosquito bites.
The ultrasound machine has even peskier problems. When it is turned on, a red bulb lights up and the device emits a quiet click or tick that represents a blast of high-intensity, ultrahigh-frequency sound that supposedly no insect or rodent can tolerate and no human can hear. By the end of four to eight weeks, according to advertising claims and customer beliefs, all mice, rats and roaches should be gone.
But many customers are dissatisfied with the ultrasound machines. Since they include the Environmental Protection Agency, the Federal Trade Commission and the U.S. Postal Service, there appears to be some trouble ahead for the high-frequency devices.
The government`s objections are based on Fish and Wildlife Service tests in Denver, corroborated by independent studies at universities and other facilities in the U.S. and Europe.
These tests have found that the devices don`t work most of the time. The ultrasonic repellers equalled the advertised claim of getting rid of pests in only one study, and that study was supported by the manufacturers.
The devices fail because the volume of high-frequency sound falls off rapidly within a short distance. The sound will not penetrate metal or plastic, and it is absorbed by walls and furniture.
Objects cast ``shadows,`` where the sound cannot reach. Pests, of course, could find these sanctuaries. To saturate a room thoroughly with ultrasound would take many such devices.
But pests are not bothered by the unltrasonic sound. In test after test, mice, rats and cockroaches showed no permanent reaction to the noise.
``Cockroaches can perceive it,`` says entomologist Roger Gold at the University of Nebraska. ``But it`s not important to them.
``Mice and rats can hear the frequency, but they quickly grow accustomed to it and ignore it.``
As a result of such findings, the government is taking action against ultrasonic devices. They`re leaving the electrocuters alone because, effective or not, they don`t produce many complaints from owners.
The EPA and the FTC are prosecuting the manufacturers of the ultrasonic repellers for misbranding and unfair and deceptive advertising, and in Indiana the state chemist`s office has banned the devices.
But what of the customers who still swear by the ultrasonic zappers? How is it that their machines get results while those of others fail miserably?
It may be faith, or pride--no one wants to admit he has been duped for $9 to $300. But whatever the reason is, it is not science.