Mosquitoes breed in standing water, and this means that if you have a pond, or even just puddles of standing water or a barrel that has filled up with rainwater near your property, you could be attracting pests via that. You can do a lot to discourage mosquitoes by getting rid of any water that you have control over, and cleaning up damp debris such as dead leaves or fallen branches. If there is stagnant water that is harder to get rid of puddles in the yard, for example, then take a moment to sprinkle some coffee grounds onto the water. This should force any mosquito eggs to float to the surface, where they will be deprived of oxygen. If you can stay on top of this and do it whenever there is water, you should eventually kill off all the mosquitoes, and no new ones will have been born.