Singaporeans waging all-out war against mosquitoes

As the number of new dengue cases rises, people are arming themselves with anti-mosquito devices to fight off the pests

With the dengue outbreak at its peak, Singaporeans are upping the ante on the war against mosquitoes.

Instead of the humble mosquito coil and insect repellent, people are arming themselves with newfangled devices that emit repelling ultrasonic and electro-magnetic waves, as well as contraptions that attract and kill mosquitoes by releasing chemicals similar to those produced by humans.

The number of new dengue cases surged to an all-time high two weeks ago, with 756 cases in a week, and a 20-year-old male died of dengue shock syndrome. So far this year, there are more than 9,000 dengue cases.

Products claiming to fight the Aedes mosquito, which spreads the virus, are sold in home-fix stores, supermarkets and department stores. Sales have risen by as much as 30 per cent in the past three weeks, says managing director Johnny Lee, 58, of supplier firm Olee International.

The company has been supplying its Pest Stop anti-mosquito products, which are from Britain, here for the past six years.

A Pest Repeller ($69.90 to $89.90, depending on area covered) uses ultrasonic technology which produces a high-frequency sound to chase away insects, and electro-vibrawaves to repel pests nesting behind walls and inside cracks, he says.

The Mozzie Magnet ($89.90 to $129.90, depending on area covered) emits carbon dioxide and mild heat to attract mosquitoes, which are then funnelled through a built-in fan into a sachet and killed.

Demand has risen by 30 per cent due to the recent dengue outbreak, says Mr Francis Lim, 58, spokesman for Mosquito Management System.

Since 2005, the company has supplied devices such as the Mosquito Slayer ($648), which simulates the human body by releasing lactic acid, octenol and carbon dioxide, and mimics the sound mosquitoes make when they discover blood. When mosquitoes go near, they are caught in a fan which blows them to a tray of solution, where they get stuck and drown.

The Biogents Mosquitaire ($350) also sucks mosquitoes into a fan, by emitting a human scent and carbon dioxide. Supplier Solbrite, which brings in the German product, declined to give sales figures.

But do these products work? Yes, for the ones that lure mosquitoes for the kill, says Dr Foo Foong Kuan, 27, an entomologist from Alliance Pest Management. "They simulate conditions that mosquitoes prefer to go to." But she says there is no scientific proof that ultrasonic or electromagnetic waves successfully fend off pests.

Electronic mosquito repellents "have no effect on preventing mosquito bites", according to a paper published in 2010 by The Cochrane Library, a publication of the Cochrane Collaboration, an interenational research body.

Mr Ng Say Kiat, vice-president of the Singapore Pest Management Association, an industry trade body, says the attract- and-kill devices may not work. If the fan which traps mosquitoes is faulty, the device may lure them to your vicinity instead, he says.

An eco-friendly option is to have anti- mosquito plants such as citronella and catnip at home.

Sales of catnip seeds have risen by about 30 per cent in the past month, says Mr Alfred Ang, 46, owner of Eco City Hydroponics. "It is for people who prefer natural methods to deal with the problem."

To make it more effective, crush the leaves and rub them on your skin or clothing so that the smell spreads, he adds.

Other plants that are also effective are peppermint, marigold, horsemint and ageratum.

But a catch-all method is best for Mr Vernon Wee, 55, chief operations officer of a security company, who recovered from dengue fever in 2005. He now uses an arsenal of anti-mosquito equipment - one which lures and traps mosquitoes by simulating the human body and another which uses high-frequency sound to repel them, in addition to mosquito coils and repellent.

Mr Wee, who lives in Toa Payoh with his wife and two daughters, had a citronella plant at home but it died within a few months. He says: "I know I cannot be 100 per cent sure but making all these preparations gives me peace of mind."

keziatoh@sph.com.sg