When does mosquito season end?

I am a mosquito magnet visiting Japan for 2-3 months in Autumn and I'm looking for some specifics on when mosquito season tends to end in different parts of Japan.

I'll probably have to fly into Tokyo, but maybe I should get the train (or ferry) straight up to Hokkaido since it's colder - would there still be mosquitoes around in early-mid October in Hokkaido?

I'm also planning to visit the Kiso valley at the end of October - being a bit more rural than a lot of locations, will mosquitoes be a particular problem there?

I assume mosquitoes won't be an issue in most of Honshu by November?

June July August. Not much outside of this.