Mosquito fogging has ‘severe limitation’: NEA

Sara Grosse, Channel NewsAsia 18 Sep 16;

SINGAPORE: The National Envionment Agency (NEA) has stepped up measures such as fogging in an effort to quell local mosquito breeding which has led to diseases such as dengue and the ongoing Zika outbreak.

But fogging has its limits, according to NEA chairman Liak Teng Lit. "When we fog, we kill not just the mosquitoes, we also kill the predators such as dragonflies. And dragonflies are nature’s air force. The dragonflies can eat as much as 100 mosquitoes a day,” he explained.

“Mosquitoes, if there are breeding sites, will recover within days. Within a week, the larvae will be flying around. But the dragonfly will take 3 to 6 months to recover. So during that period, there will be no predator to control the mosquito.”

Added Mr Liak: “So fogging, while it has some use - and quite frankly, it looks very impressive and lots of people like the fireworks; because of all the smoke, looks like something is being done - but there is severe limitation."


The most effective method to reduce the mosquito population remains that of eliminating potential breeding habitats.

Said Assistant Professor Roman Carrasco of the Department of Biological Sciences at National University of Singapore: "They have evolved to be able to reproduce very fast in houses, outside of houses and they are very effective in detecting stagnant water that one might have in the garden or the house, or some hidden crevice in a tree.”

"They are very good at finding these spots for breeding and once they are able to find the spot, they are able to lay hundreds of eggs and the females have been effective at finding people to bite.”

“That is why it is so hard to control them - because a few mosquitos are able to make the most of the very few breeding habitats and maintain a population that is enough to continue having dengue or Zika," he added.

Between January and July 2016, NEA officers were deployed daily to do about 748,000 island-wide inspections, of which more than 10,000 breeding spots were destroyed. Half of these were found in the home. With the Aedes mosquito preferring to breed in clean, stagnant water, some two thirds of breeding sites are found in homes.


Over the past two years, the top five breeding habitats in homes have not changed. They are domestic containers, such as pails; flower pot plates; ornamental containers such as vases; hardened soil in plants and toilet bowls.

With the majority of breeding spots found in homes, in some cases, authorities may need to gain entry into inaccessible premises by force, in order to inspect. In these cases, NEA is urging all residents to be fully cooperative.

"Frankly, there are times when the NEA officers turn up at the door, people are at work, so we have to come back again, usually in the evening. But even in the evening sometimes people they are not there. And there are also households that are empty. And there are also people who have gone for holiday,” said Mr Liak.

“So we need to create the urgency for people to realise that this is a problem. And I think the best thing for everyone to do is actually this. First, when an NEA officer comes by, please co-operate. Please help. Open the door because they are very busy going house to house.”

“Number two, if you are not going to be at home for a few days or a few weeks, do leave the key with your neighbours. And when the NEA officer comes, get your neighbours to open the door. Then we don't have to force entry."

- CNA/jo

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