Mosquitoes find breeding areas around your home and begin to multiply in numbers. Typically gardens with large vegetation such as trees, shrubs and bushes develop a mosquito problem over time. Other sources include stagnant water from pot plants, buckets, ponds, etc. It is also common for the breeding areas to be in neighbouring properties which can make control difficult.
If the breeding sites are located on your property mosquito reduction and control is more likely, otherwise treatment will only have a limited effect.