Mosquitoes are the biggest killers of humans on this planet. They transmit deadly diseases such as malaria, dengue, chikungunya, yellow fever and West Nile virus. And therefore they deserve the death penalty. As swatting all of them would be quite an impossible task, we use insecticides to kill them. Mosquitoes, especially those that transmit malaria, are mainly targeted with insecticides applied in/onto bednets (so-called insecticide treated nets or ITNs) and insecticides sprayed on walls inside houses (indoors residual spraying, or IRS).
Mosquitoes are the biggest killers of humans on this planet (...) and therefore they deserve the death penalty
In sub-Saharan Africa alone the total number of ITNs that have been delivered during 2012-2014 is estimated to be over 400 million. For IRS 870 metric tons of public health insecticides have been used between 2000 and 2009.
An additional 12 tons of chemicals was distributed for the (re)treatment of ITNs (ref 2). So we certainly try to kill these mosquitoes. But why does malaria continue to be such a massive problem? And why are we seeing an increase in malaria cases again in certain areas?
In sub-Saharan Africa alone the number of ITNs that have been delivered during 2012-2014 is estimated to be over 400 million
Well, first of all, throwing such vast quantities of insecticides at the mosquito problem results in the emergence and spread of insecticide resistance. By changing their metabolism or the target sites of insecticides, mosquitoes can suddenly survive long exposures to chemicals. Unless proper resistant management strategies are in place, such as the rotation of chemicals or the use of insecticide-mixtures, resistance is sure to surface sooner or later (probably sooner).
In addition, mosquitoes are able to change their tactics. By starting to bite earlier in the evening, before people go to sleep, they avoid having to deal with bednets. By biting people outside, they avoid bednets and those chemicals we spray on the walls. And these mosquitoes are extremely difficult to target, as we do not have tools as powerful as the indoor-based ITNs or IRS for those outdoor villains.
Mosquitoes can survive long exposures to chemicals
Finally, we are dealing with several petty criminals: Mosquitoes species that have always been ignored because there were only a few individuals transmitting malaria. But now that we are moving from malaria control to malaria elimination, they suddenly become important. Unfortunately, being largely understudied, we do not know much about their whereabouts and habits, making them difficult to target.
The huge problem with mosquitoes is that there are so many of them, which makes it relatively easy for them to adapt to a new situation: There are always a few outliers that are not affected by our interventions, which can then quickly grow in numbers. So if we do not design our mosquito hunt strategically, they will easily outsmart us. We continue to sentence them to death; they continue to break out of jail.