> How could we kill all mosquitos without killing all other insects?

Narrowly tailored insecticides are actually quite feasible. They are just quite a bit more expensive to develop than the indiscriminate kind so we rarely do so.

The key for a narrowly tailored insecticide is to base it on the hormones that regulate the insect's behavior. Insects are in many ways like little biological robots with a bunch of preprogrammed subroutines built in, with hormones triggering calls to those subroutines.

Say you have an insect that on the first summer evening above some certain threshold temperatures forms swarms two meters above patches of blue flowers next to ponds, where it mates, then the females lay eggs and die.

All those steps will be triggered by hormones. If you can identify the hormone that is released by the summer evening hitting the temperature threshold and synthesize that, then you might be able to spray an area with that hormone during the spring. That can then trigger the whole sequence of swarming, mating, egg laying, and dying to start early--before the weather is warm enough for the eggs to by viable, or even before the insects of reached sexual maturity so that the mating does not even produce fertilized eggs.

There are at least two very good things about this approach.

1. The insects do not evolve immunity.

2. The hormones for one insect are generally not harmful to things that eat those insects. Since those hormones already occur naturally in the insect, their predators are already exposed to them. All we are doing is messing with the timing.

These are expensive to develop because you have to really know the target insect. You need people to study its lifecycle in detail to identify what subroutines it has in its little insect behavior library. You need to identify the hormone triggers that affect the behaviors that you might want to use.

You probably also should verify that you have right insect. There was a case where an invasive species of moths (I think) was devastating crops in one state. In the state the moths were native to they were naturally kept under control by a parasitic wasp species that was also native there. An attempt was made to import the parasitic wasps (this was deemed low risk because the wasps could not survive without the moths, so once the invasive moths were gone the wasps would die too).

It was a good plan, and it would have worked except for one little detail. It turned out that there were actually two species of parasitic wasps that were almost indistinguishable. Only one of the two was a parasite for the invasive moth species. The other was a parasite for a different moth.

It wasn't until after the imported wasps failed to do anything about the moths that entomologists took a closer look and realized there were two species, and all the wasps that had been trapped for export to fight the moths had been collected in a place that had the wrong species.

Anyway, the bottom line is that you have to know your target really well to do the hormone based approach. And because it is so effective you can easily end up with an insecticide that will wipe out most of the target in a region, so you don't get repeat customers until maybe years later when the insect starts to make a comeback.

So you end up with an insecticide that was expensive to develop, might have a highly variable market, targets just one species, and most of the R&D for it does not really help with the next one you develop for the next species. That's just not economically worth it in most cases for most insecticide companies.

It might be worth it in this one case, though, perhaps as a publicly funded project. A lot would depend on how many different species of mosquitoes are involved. If only one or two are responsible for most malaria spread, it could be worth it. If there are dozens that are significant spreaders it might not be feasible.