ExOfficio makes mesh shirts with mosquito repellant (so that you don't have to keep reapplying bug spray). They have long sleeves with thumb holes that cover the tops of your hands and they (crucially) extend down in the back to cover your lower back/upper-butt when you crouch down.
(Not sure where to put this, but mosquitos aren’t very good fliers, so if you’re in mosquito country, try to plan excursions when it’s breezy out, and if you’re on the porch, bring out a fan and set it to oscillate around the area where folks are seated)