Not just any long sleeve shirt
If you are like me, insect repellent is not an item to be carried. It can leak, it can run out, it can poison you and worst of all- it doesn't work!!!( without applying every 10min)
I cannot be bothered personally to be toting around a liquid other than my water. While It may seem I never have a long sleeve shirt on, I can assure there is one in my pack or fishing box close by.
Your long sleeve shirt is versatile. It protects you from the sun and the cold. If it has a high enough thread count, it can also make it much harder for mosquitoes to bite you. A good long sleeve shirt for your Amazon River travels has the following qualities-
1. Light weight , quick drying
2. Fits loose ( not flush with the skin) so mosquitoes can't bite
3. Of lighter colors ( black is a no no for mosquitoes and the sun) the dark color absorbs more heat. Dark also attracts more mosquitoes and makes them feel secure to feed more without detection.
Of course a long sleeve shirt is not a magic bullet. There are areas that are still at risk like the shoulders and neck where the cloth fits snug against the skin. It are these tight fitted areas that the mosquitoes can take a quick drink.
If you spray a bit of permethrin repellent in the tight fitting areas,you should be ok.
Don't forget to consider these things when you go to buy a long sleeve shirt for the Amazon. Don't expect to be 100% insect bite free just because of a long sleeve shirt. Choosing carefully can help a lot .
and.... Don't forget to take plenty of water- it is hot out there