I heard about this a few months ago and have tried this and so has several of my friends. It really works. Listerine. Pour it on a wash rag and wipe down with it or put it in a spray bottle and spray it on. It worked 100%! I couldn't believe how they buzzed all around me but not one landed for their blood sucking dinner. If you are going to be out long term, put it in a small spray bottle and take it with you. It does wear off after about 25 to 30 minutes so having a spray bottle handy to refresh works great if you are sitting out at night.
Hope this helps you enjoy sitting out at night this summer!