taken from HortIdeas
High-Frequency Mosquito “Repellers” Found Ineffective
This isn’t the first time we’ve reported on scientific trials of electronic devices claimed by their distributors to repel mosquitoes due to high-frequency sounds, and we suppose it won’t be the last time, either. As long as people long for a simple and inexpensive non-chemical solution to mosquito bites, there will no doubt be marketers ready to provide that solution … whether or not it actually works!
The latest trials, conducted in Brazil, included six electronic mosquito “repellers” made in various countries, including one called “Mosquito Guard” from the U.S. and a freeware computer program from Thailand. Most of the devices produced sounds at or above 10,000 Hertz (cycles per second), in the high range of human hearing (and beyond the range of hearing of many older people) but below or at the bottom of the ultrasonic range (typically defined as upwards of 20,000 Hertz).
It is at least a little humorous that literature included with some of the devices links mosquito repellency of sound to the wing beating frequency of the insects, which (although the literature doesn’t say so) has been shown to range between 400 and 900 Hz, far below the frequencies of sounds produced by the “repellers.”
Over a 10-minute period, attraction of mosquitoes to a person’s hand was statistically the same whether any of the devices (located nearby) was turned off or on. In some cases, there was slightly more attraction when on. These “repellers” don’t repel!
Reference: Isa__as Cabrini (Universidade Estadual Campinas, Instituto de Biologia, Departamento de Parasitologia, Cx.P. 6109 Campinas, S_
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