Chemicals alone cannot control mosquitoes in Dhaka city
Different species of mosquitoes behave differently in terms of the breeding season, life cycle reproduction, resting and behaviour. Therefore, the management process of each species is different and we cannot apply the same strategy for all mosquitoes
Every year, we spend at least Tk5,476 crore to kill mosquitoes.
For the fiscal year 2020-2021, the Dhaka North City Corporation approved a budget of Tk70 crore for mosquito management programmes.
The Dhaka South City Corporation has also allocated Tk300 crore for integrated mosquito management work.
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And then there is the million-taka industry of mosquito repellents.
Yet come winter time, Dhaka residents are left struggling with not just the menace of mosquito bites, but also potentially fatal mosquito-borne diseases like dengue and chikungunya.
This happens because there is a gap between proper planning and execution in mosquito management.
Till now we have recognised around 123 species of mosquitoes in Bangladesh and among them, 14 species were identified in Dhaka city.
However, there are four genus – Culex, Aedes, Mansonia, and Armigeres – that are more common. Currently, 95% of the mosquitoes that we see are Culex species.
An outbreak of Aedes might happen a few months later. Each insect has its own behaviour patterns in terms of the breeding season, life cycle reproduction, resting and behaviour.
Therefore, the management process of each species is different and we cannot apply the same strategy for all mosquitoes.
The mosquito control authority needs to apply an Integrated Vector Management (IVM) plan for Bangladesh of Dhaka city for successfully controlling the mosquitoes.
The four pillars of IVM are explained below:
Environmental management: It is the first pillar for the management of mosquitoes. Each species has its own breeding places. These breeding places should be managed first by a breeding source management and reduction programme.
For the management of Culex mosquitoes, we need to clean drains, ditches, ponds, puddles, and lakes.
Aedes mosquitoes breed in containers, therefore containers should be removed or the water in them (if any) should be changed every seven days.
It is also important to clean clogged drains and lakes.
Biological control: We need to control mosquitoes using biological control agents. We can easily culture and release Guppy fish and bacteria into the polluted water to control Culex, and for Aedes, we can release copepods (small crustaceans) into the Aedes breeding water.
Chemical control: As we know, mosquitoes lay eggs in water which then turn into larva, pupa and gradually become adult mosquitoes.
Chemical control can be easier at immature stages, like egg and larva.
Larviciding should get priority instead of fogging. Fogging may be applied when adult mosquitoes are available in the environment.
Fogging kills up to 90% of mosquitoes in the lab but in the field, it may be only 30%-35% effective because some factors work as inhibitors.
Wind velocity, machine's discharge rate, carrier's movement speed, and wind direction are factors why we cannot get good results from fogging and these four components cannot be controlled. So we should focus more on larviciding.
Community involvement: Without the participation of the community, the mosquito control programme will not be successful.
City dwellers should participate in association with city corporations for this programme.
City corporations should make people aware of their responsibilities – not dump garbage in puddles or ponds and keep pots or containers clean and upside down.
Once we can adopt these four pillars equally and create coordination among these, we will be successful.
We have observed that city corporations focus on chemical control more, but this alone cannot ensure controlling mosquitoes in Dhaka city.
Hence, the mosquito control authority needs to make IVM macro and micro operational plans for both Aedes and Culex and it should be executed all year around.
For example, a particular ward's mosquito surveillance (breeding place and adult) should be conducted first to specify the places and detect the species.
After surveillance, macro and micro plans should be aligned with the four pillars of IVM and executed. Meanwhile, the monitoring and evaluation of this programme is recommended.
For the successful implementation of the IVM plans, we need skilled manpower.
Mosquito management staff should be trained about the species of mosquitoes, breeding place, types of chemicals, doses, and also machines.
They should also be awarded as per their performances.
Mosquito management is not a job, it is a challenge, a service – which they are providing to us. So, keeping them motivated should be the trick, I believe.
Moreover, expert entomologists' advice can direct the authorities to sketch the macro and micro operational plans to control mosquitoes and for that, we must continuously stick to those plans for the next five years.
Kabirul Bashar is a professor of Entomology at Jahangirnagar University
