For those that live in sub-tropical or tropical countries, mosquito buzzing and biting is a common nuisance. Some of them are the carrier to diseases, such as dengue fever vectored by Aedes aegypti. The ways to control mosquito populations warrant a full-length novel. In Malaysia, the most common control measure is insecticide spraying.
Optimal insecticide spraying time
At where I stay and worked, insecticide fogging is carried out twice a month, in the least. This high frequency got me thinking of whether such high frequency works in controlling the mosquito population and whether there are works done by scientists on when best to conduct fogging for best results.
Mika Oki and colleagues did a simulation study to model when is the optimal time to do fogging. Their study is unique in terms of they take into account the effect of seasonality (= to spray in Wet or Dry season) and population immunity (= how susceptible were the population to dengue fever?).
Wet season and early is the key
Current spraying felt to me like it is a knee-jerk reaction with regular scheduling. For example, my apartment complex has foggers coming the second and third week of the month, Tuesday and Thursday respectively. This is perhaps not the best way to control dengue outbreaks. After all, female mosquito doesn’t follow a regular second Tuesday and third Thursday to come out and bite people.
In fact, earlier study suggests insecticide should be carried out during the peak of dengue outbreak. But Oki simulation results debunk this myth and revealed that the optimal timing has to be earlier – between the start of the dengue season (usually in wet season) and the height of the outbreak peak, NOT on the outbreak peak and after, or every second Tuesday and third Thursday of the month!
Oki M, Sunahara T, Hashizume M, Yamamoto T (2011) Optimal timing of insecticide fogging to minimize dengue cases: modeling dengue transmission among various seasonalities and transmission intensities. PLoS Negl Trop Dis 5(10): e1367