The transmission of mosquito-borne diseases such as dengue and Zika is sustained by infected Aedes mosquitoes and infected humans. When an infected mosquito bites an uninfected person, it passes the virus on to that person. In turn, when the infected person is bitten by an uninfected mosquito, that mosquito becomes infected and capable of spreading the virus to other uninfected individuals. As such, source reduction is key, as it will prevent the breeding of mosquitoes. 

In the event of an outbreak or when there is a high population of adult mosquitoes, chemical control methods such as the use of pesticides, can complement source reduction efforts. Pesticides come in various forms. Aside from killing adult mosquitoes, pesticides such as Bacillus thuringiensis israelensis (Bti) and sand granular insecticide are effective in killing mosquito larvae. It is recommended that Bti or sand granular insecticide be added to potential breeding habitats such as vases, roof gutters, gully traps, drains and other places where water cannot be removed. Temephos, the sand granular insecticide which is applied to drains by NEA officers, is similar to the sand granular insecticide that we advise homeowners to put into their flower vases or other water-containing receptacles. The active ingredient of the insecticide does not have a long residual effect on the environment, and the concentration used is low and deemed safe by the World Health Organization (WHO).