I went on this holiday in October 2010 and don't remember coming across any mosquitoes. Like Denise, if they'd been around they would have found me.
I think Just You are trying to cover absolutely everywhere in the notes. I suspect the trouble spots would be anywhere marshy but there was only one such area that I remember in Tuscany and that was the walk from the hotel on the coast across to the main town a bit further inland, and I did that on a blazing hot day with only birds and butterflies around.
Have a lovely time - I'm jealous.
Ann