A 2007 study determined that high-frequency machines do not repel mosquitoes.
Gardeners and anyone who spends a lot of time outdoors in the spring and summer commonly fight insect onslaughts. Drawn by perspiration and scents, insects swarm during warmer weather. Sprays can stink, and long clothing isn't always a viable option, so some people seek to repel insects through machines that emit high frequencies. The idea is that the ultrasonic sounds bother insects and they will fly away from it. However, scientific studies repeatedly have questioned whether such devices are effective. Does this Spark an idea?
Theory Behind Frequencies to Repel Insects
Machines that emit ultrasonic sounds produce noises so high-pitched that they are undetectable to the human ear. Proponents of machines claim that the devices do several things to repel insects. First, the machines mimic predators, which scare away insects. A mosquito, for example, may think a predatory dragonfly is nearby. Moths may believe a bat is swooping down to feed. Some products also claim that the sound mimics male mosquitoes, and that the biting females will flee, having already mated during the season. High-frequency sound machine manufacturers claim that the frequencies prompt insects to leave the area immediately without harming or inconveniencing humans in the process.
Types of Machines Available
There are several types of machines available that emit high frequencies to repel insects. Some are backyard versions meant to cover a large area. These can cost more than $100 to buy and maintain. Manufacturers also product hand-held devices, sold for a fraction of the cost. Some units are smaller and meant to be used nearby a person who hopes to keep insects at bay. Others are devices that double as key rings.
Studies Question Effectiveness
A series of studies have called into question whether high frequencies keep away insects, especially mosquitoes, when they are targeted with electronic mosquito repellents (EMRs). A Rutgers University entomology professor said claims that the machines repel mosquitoes "border on fraud." Another professor from Mazandaran University of Medical Sciences in Iran, who led an international study on high frequencies used to repel mosquitoes, said that there was "no evidence to support [EMRs'] promotion or use." Females seeking a host to feed from, the experts said, will not be repelled by EMRs and do not hear well enough for the machines to have any effect.
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