peter goes with a short sleeve merino top with collar from Minus-33 layered under a nylon or polycotton long sleeve shirt. this is the lightest combination that i have found that will run cool enough on hot days, and not be all chilly and temp swinging (annoying) in cooler weather.
bug are not able to penetrate this combination. they will however eventually drill thru almost any form of single layer nylon shirt. this will be most often in the rear shoulder area.
permithrin alone on merino will be found to be partially effective. absolutely much better than untreated. but it's going to fade fast on your back. remember that one of the "pluses" to permethrin, the thing that keeps it acceptably safe, is that it neutralizes quickly when exposed to sweat. sooo .. you're right back to getting nailed right thru the merino.
you can ALWAYS use another merino wool short sleeve top. i know if i had 6 of them i could wear them dialy. so it's not really a "backpacking purchase" .. not really ...
and you probably already have a long sleeve shirt of the collar and buttons variety.
so seee .. it really won't cost a anything to try this.
if bugs going to be Epic : ... yes. spray everything with permethrin as suggested. do that.
(maybe not spray the tent fly. i think it wrecks them)
- sew half the cuffs closed.
- sew velcro to the remaining opening. (convenience in getting dressed in the bush i;ll tell you )
- install extra cuff buttons/snaps to close down the wrist opening even more.
that ought to do it shirt wise. shirts marketed along the lines of hiking/treking often have an additional mesh liner in the shoulder yoke. the liner adds another layer of depth. it's a good thing.