My guess was they were some type of bee. Jim, my friend and our guide, who also keeps bees at his home near Ames, concurred that they were likely a type of bee. When we got back to our resort, I went online and did a little research. There are many species of the stingless bees in Costa Rica, Apidae Meliponinae, and a little research will show similar bees to these little golden ones shown above. Many will create the tube entrance to their hive. Though stingless, they will ward off intruders by massively flying at the intruder, getting into eyes, hair, ears, etc.
One site indicated that though small, and unable to produce the quantities of honey when compared with the European honey bee, the ease of working with them makes them very attractive in Costa Rican apiaries. Partly this is also because of the strains of Africanized bees they would work with otherwise.
I found them very interesting, especially discovering that they are actually kept for their honey production. A couple of interesting links follow:
Costa Rica Apiaries
10 Degrees Above