"every member of the ecosystem plays a role in sustaining the ecosystem" is not entirely true - there are many members of the ecosystem (including this particular species of mosquitoes) that provably are
not required to sustain the ecosystem, because they're invasive species who clearly weren't needed to sustain that ecosystem which was just fine before they arrived. In many cases (though not this one) the invasive species actively contributes to destruction of the ecosystem, so preserving the ecosystem may require to fully eliminate a particular species from it.
Most members of an ecosystem play a role in sustaining it, but certainly not all.
