In reply to ianto:
Lima is generally way too dry for mosquitos, and at this time of year its too cold.
I met a taxi driver in Lima who told me about his first visit to Cusco when he was 18. He noticed that water fell on the pavement, and then the bits of water joined up and formed little pools on the street. He was 18, and seeing puddles for the first time.
In Lima you get a coastal mist for months on end during our summer (if you know east coast Scotland, you will recognise it as haar). But he had never experienced rain until he went to Cusco.
In the mountains its too cold for the mossies.
What you plan is very benign from a disease viewpoint. Apart from tummy bugs, of course.