The problem with spraying against mosquitoes is that it also kills many other insects upon which we rely (e.g. for pollination) or which we like because they are pretty (e.g. butterflies). Where I am staying it is not allowed. Local conservationists claim most mosquitoes in the resort, which have a pretty narrow range of hatching requirements, are bred by people. They breed in swimming pools that have not been properly drained in the autumn, and in puddles in people's gardens formed in junk that hasn't been disposed of yet. Well, that's what they claim. Believe or not as you will.