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Nannotrigona sp.
These tiny guys make entry "tubes" into the tree. They look like they are made of wax. The insect itself is quite small, maybe a 1/4" long max. They are mostly black. You can see some at the entry. They were all working on the tube structure.
Tropical dry forest. I have seen them in both living and dead trees.
Please also consider adding this spotting to the Animal Architecture mission at http://www.projectnoah.org/missions/8082...
Those look like stingless bees. If anyone can ID them to species it would be JuanDiTrani.