Are ultrasonic mosquito repellent devices as effective as their manufacturers claim?
The Consumer Council has probed into the claims made by manufacturers of these devices that they can repel biting mosquitoes effectively.
These products are designed to emit sounds that mimic male mosquitoes and dragonflies, thereby supposedly frightening away the biting female mosquitoes.
The Council has written to six of the local suppliers of ultrasonic electronic mosquito repellers for evidence to substantiate their efficacy claims. Five suppliers have responded but only two were able to produce laboratory results of some sort.
The evidence provided indicated that even with the use of ultrasonic repellers, mosquitoes were still found to fly into a laboratory-controlled space despite there were comparatively fewer mosquitoes than those in an identical space without the repellers. The efficacy of the devices involved when operating in actual environment remains an issue for further investigation.
The efficacy of ultrasonic pest-controlled devices has long been an issue of concern.
In the United States, the Annals of Internal Medicine (1998) and the Centres for Disease Control (CDC) have separately drawn the conclusion that ultrasonic devices were not effective at preventing mosquito bites.
Further, in 2001, the U.S. Federal Trade Commission (FTC) has issued warning to over 60 manufacturers that they must support their claims with competent scientific evidence.
Between 1985 and 1997, the FTC brought law enforcement actions against six companies that allegedly made false and unsubstantiated claims about the effectiveness of ultrasonic devices in controlling rodent and insect infestations. All cases were resolved by consent agreement.
According to the Food and Environmental Hygiene Department, at least 70 species of mosquitoes have been identified in Hong Kong, and it is therefore unlikely that anyone ultrasonic device is totally effective against all of the various species.
The Consumer Council would like ultrasonic products against mosquitoes on sales in Hong Kong to produce independent scientific evidence to support their efficacy claims.
In this May issue of CHOICE is included a comprehensive report on the various types of mosquito repellents commonly in use by consumers.
Both the U.S. Annals of Internal Medicine and CDC have recommended the use of DEET-based products. DEET is labelled also variously as N,N-diethyl-meta-toluamide, Diethyltoluamide, N,N-diethyl-m-toluamide and N,N-diethyl-toluamide.
But a high concentration of DEET is not recommended for casual use. Under most conditions, repellents with 10% to 35% DEET will suffice, and that repellents used on children should contain no more than 10% DEET.
Consumers are reminded to look for the prescribed registration number "HK-XXXXX", which should appear clearly for easy recognition on the outside of the package of insect repellent products containing western medicine intended to be applied on the human body, such as mosquito repellent aerosols or mist.
Pesticides which are ready for immediate uses and for general domestic uses, such as mosquito coil and mosquito repellent patch, should bear the registration number "1PXXX".
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