Sunday September 11, 4:17 PM
Current fogging practices ineffective
in killing the Aedes mosquitoes
SINGAPORE: In the war against dengue, current fogging practices may
be ineffective in killing the Aedes mosquitoes.
The World Health Organization (WHO) has advised that fogging at
dawn is most effective.
But according to the Singapore Pest Management Association, most
fogging here is carried out after 10am or in the afternoons when
most Singaporeans are at work and away from their homes.
Mosquitoes may be killed when they come into contact with the
fogging fumes but fogging done during these times is not very
effective for several reasons.
One, ambient temperature is higher in the day and hot air causes
the fumes to dissipate faster.
Two, more air drafts in the day carry the fumes away from intended
target areas.
"You can actually fog anytime during the day because the Aedes
mosquitoes are active during the day time and they bite throughout
the day. But of course, peak biting is during dawn and dusk. So, it
is more beneficial to fog during these periods because you have a
bigger abundance of mosquitoes around," explained Christina Liew, a
medical entomologist at the National Environment Agency
(NEA).
So is fogging as it is currently done just a smokescreen?
"The end user insists that fogging be done because he is being
harassed by mosquitoes. So when he sees that there is lots of smoke
going on, he is happy that something is being done. The pest
company knows it is ineffective doing it. I have heard stories.
Some just add kerosene to water so that when you fog, you still get
white smoke coming out. In fact, it's all for show, " said G.
Surajan, president of Singapore Pest Management Association.
Responding to Channel NewsAsia's query, NEA says it does not know
of any pest control companies which have been adding kerosene to
water. And it will take action against any who has done so.
So why don't pest companies carry out fogging at dawn or
dusk?
They say cost is an issue. Pest companies have to pay their workers
one and a half times more in overtime pay if fogging is done
outside the standard nine to five work day.
And most town councils, private condominiums and construction
companies will only award fogging contracts to the lowest
bidder.
There is another reason why fogging is done when the sun is high -
pest management companies say Singaporeans complain of noise
pollution from fogging at dawn.
Biologists have also warned that fogging, if conducted at
sub-lethal dosages, will cause mosquitoes to develop resistance to
the pesticides used.
But it is not known if all fogging carried out here is at the
appropriate lethal dosages.
(source: Yahoo Singapore News)
