"Ecological usefulness" appears to be shorthand for a measure on a species' critical interconnectedness. That is to say, the magnitude of the impact on other species a particular species' removal would have. If you knock out algae, you wipe out many ocean species. If you knock out certain mosquitoes, you may only jinx malaria.

Wrong. Again and again repeating the same wrong idea.

Mosquito larvae are aquatic, and the prey of freshwater fishes, toads, frogs, bats... they are directly or indirectly linked with almost everything around marshes and lakes: bacteria, algae, birds. We can expect a tsunami of unpredictable consequences for freshwater ecosystems and also for men. What if we wipe mosquito only to discover that they are necessary to controlling amoeba proliferation in water, for example?. We don't know.

Yes