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NewsAsia 14 Oct 05 Ovitraps effective in destroying mosquito larvae By Hasnita A Majid, Channel NewsAsia SINGAPORE : The number of dengue cases may have dropped lately, but the authorities are not resting on their laurels. They are pushing out a pilot project using ovitraps, devices that trap mosquito eggs, in Marsiling. Some 500 ovitraps will be placed in common areas and inside homes within Marsiling over the next three months under the pilot study to track mosquito breeding habits. Mosquito eggs laid in the ovitrap will drop through a fine wire mesh floating on the water surface. When they hatch, the mosquitoes will be trapped and therefore drown. Said Dr Christina Liew, senior research scientist at the Environment Health Institute, "We found that it's very effective in detecting mosquitoes when we have not seen any adults flying around." But it's not 100 percent foolproof. Said Dr Liew, "The float ring can get stuck at an angle and this will become a very attractive breeding source for mosquitoes. We can't afford to put it out to the public in case this happens." So for now, it will only be used by town councils. Costing S$15, it is usually put in dark areas and aims to replace the natural breeding habitats of mosquitoes. Using the ovitrap is one way of destroying mosquito larvae that is laid in water. But one problem is that mosquitoes can also lay eggs on damp surfaces and the eggs can stay unhatched for up to nine months, until some water comes their way. However, there must be enough moisture for the eggs to absorb to remain dormant. Said Dr Liew, "The Aedes eggs actually do survive desiccation for many, many months in the wild and in the lab. What we found is that after nine months they can hatch out for routine colonisation; it's just a biological mechanism. But that's only true for Aedes eggs and the Anopheles; for Culex eggs, they don't survive desiccation. That is a huge problem, especially in forested areas; so I think again the important thing is to concentrate on source reduction." To help households destroy the Aedes mosquitoes, a device similar to the ovitrap, called the gravitrap, will be made available to the public in a few months. It not only traps the mosquito larvae but also the female mosquitoes that lay the eggs. Dr Liew said, "EHI, the research arm of NEA, has come up with the prototype of a lethal ovitrap which is very effective that can capture the ovum depositing female and hence the 300 larvae that she can potentially lay in her lifetime. We are in the midst of developing this and manufacturing it." An ovitrap project was carried out in Bukit Panjang two years ago, but was stopped when SARS struck. Results showed that the number of Aedes larvae collected reduced gradually over the four-month period when the project was carried out. - CNA /ct links Related articles on Singapore: dengue issues, policies, discussions |
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