We thank Mr Joe Teo Kok Seah for his feedback and suggestions on fogging ("Time fogging to get maximum benefits"; Monday).
The National Environment Agency (NEA) provides guidance to pest control operators that fogging should be carried out in the earlier part of the morning or later part of the afternoon.
This is because ambient temperatures during these times are lower, hence allowing the fog to stay at ground level longer; the Aedes aegypti mosquitoes are also known to be most active then.
Therefore, fogging at such periods of the day optimises insecticide contact with mosquitoes.
We will remind pest control operators of this good practice.
In areas with active transmission of Zika and dengue viruses, NEA carries out vector control operations to remove mosquito breeding habitats.
It also conducts indoor spraying of insecticides and outdoor fogging to kill adult mosquitoes, as well as oiling of stagnant water, for example, in drains, to kill mosquito larvae.
As the Aedes aegypti mosquito tends to hide and rest indoors, indoor misting or spraying of insecticides is just as important as outdoor fogging.
These methods are, however, effective only if the insecticide has direct contact with the mosquitoes. Thus, application of such insecticides has to be repeated frequently, as new batches of mosquitoes will continue to emerge until all breeding habitats have been found and removed.
Hence, routine fogging is not a sustainable vector control measure, and source reduction is still a more effective and sustainable strategy.
In non-cluster areas, source reduction is also the most effective mosquito control measure for keeping the mosquito population low.
Detecting and removing breeding habitats and killing larvae help eliminate the mosquitoes at the most vulnerable stage of their life cycle. This is in line with the World Health Organisation's recommendations for vector control.
It is therefore important that premises owners undertake vector control measures regularly, and ensure proper housekeeping within their premises at all times, to remove potential mosquito breeding habitats.
Residents also need to do their part to prevent mosquito breeding in their homes by doing the Five-Step Mozzie Wipeout regularly. T
Director, Environmental Public Health Operations
National Environment Agency