Some mosquitoes respond to vibrational devices by biting more.
When you flinch or freeze at a sudden and unexpected stimulus, you're experiencing a startle reaction. A startle reaction may be as minor as blinking to protect your eyes from wind-blown debris or as urgent as racing for cover after hearing an unidentified loud noise. A defensive response to noise, known as acoustic startle, prevails throughout the animal kingdom. Its effect on a handful of insect species has led to the marketing of numerous devices that use sound vibrations to repel insects. Does this Spark an idea?
Negative Phonotaxis
Negative phonotaxis occurs when acoustic startle causes an insect to move away from a sound. It's also the principle behind the design of vibrational insect repellent devices. These machines or collars produce ultrasonic or subsonic vibrations to frighten insects away. Their manufacturers promote them as environmentally safe, inexpensive and permanent alternatives to chemical insecticides.
Insect Hearing
The human eardrum responds to sound vibrations between 20 hertz and 20 kilohertz. Several insect species have tympanic organs, which are air-filled cavities covered with thin tissue resembling the human eardrum. Insects with tympanic organs react to ultrasonic vibrations higher than 20 kilohertz. Many depend on these organs to help them avoid bats hunting with ultrasound signals. Night-flying moths and butterflies, as well as crickets, locusts, green lacewings and praying mantids belong to this group. Research suggests that some beetles and flies also have tympanic hearing. Cockroach and mosquito antennae have sensory hairs responsive to ultrasonic vibrations.
Ultrasonic Repellent Research
Extensive laboratory testing suggests that vibrational insect control devices don't live up to their manufacturers' claims. One study published in "Entomologia Experimentalis et Applicata" in 2007 indicated that a device producing ultrasonic vibrations between 20 and 100 kilohertz did nothing to discourage mosquitoes and German cockroaches. Researchers at Brazil's State University of Campinas found that three commercially available machine operating at ultrasonic frequencies between 9.8 and 18.2 kilohertz actually caused mosquitoes to bite more frequently. Findings from a University of Florida study presented in the December 1990 "Journal of Economic Entomology" states that fleas on cats wearing ultrasonic repellent collars for a week lived as long and produced almost as many offspring as fleas on cats in the control group.
Subsonic Insect Repellents
Subsonic insect repellents produce sound vibrations below 20 hertz. Their makers claim that insects find these devices more annoying than ultrasonic repellents.
Limitations
Vibrations from both repellents typically lose 50 percent of their power after traveling only 15 feet, according to Rutgers University Research and Extension. They dissipate completely after 30 feet. A second problem is that furniture and large appliances create acoustic shadows, blocking sounds from reaching the insects they conceal.
Tags: sound vibrations, ultrasonic vibrations, acoustic startle, between kilohertz, fleas cats, have tympanic, human eardrum