We rented a place for a week to the north of Bordeaux, outside of Saint-Andre-de-Cubzac. It was late Spring, mid to late June, 2003. We ate dinner outside our gite each night, and mosquitos weren’t a specific problem, but when we slept with the bedroom window open the first night (no screen), other bugs virtually ate us alive during the night, and we kept the window closed after that. Insect repellent wouldn’t be a bad thing to have, or to pick up over there. Maybe things have changed a bit since 2003, but other places we’ve stayed in other parts of France haven’t had window screens, either, and were otherwise very nice places.
For what it’s worth, 3 years ago in Pont Aven, Brittany, as people gathered near the water for the Bastille Day fireworks that evening, “moustiques” came out and starting sucking blood. The wind picked up a bit and blew away the mosquitoes, so the evening was saved!