Basically you have three interventions that you need for malaria control. First is the nets. Then there is the treatment: you eliminate the parasites in the blood of the patients, and you spray insecticide inside the houses, which also kills the mosquitoes. You're right that it's only one species of mosquito, the anopheles, that transmits the malaria, but the combination of these three interventions can basically cut that down.
We see that already in places like Zanzibar, where the reduction of malaria transmission is not 50%, but 90%. If you do all three interventions in a defined area, then you can see dramatic declines.
By the way, I just want to note that there are other mosquitoes, and you can kill those at the same time. That will not prevent malaria, but aedes, for example, transmits yellow fever or dengue fever, or others. You have positive side effects there as well, because you're killing other types of mosquitoes at the same time, so it's quite a dramatic effect that you achieve with relatively simple and doable interventions.
Thank you.