The two sister species, one from Coiba Island in Panama and one from northern Colombia, descend from a group of stingless bees that originated in the Amazon and moved north over millions of years, eventually to Mexico.

The bees have a limited migration range, since worker bees must build a new nest before a virgin queen will move in to form a new colony.

“It’s really impossible for them to get across a water barrier,” said David Roubik, an entomologist at the Smithsonian Tropical Research Institute and one of the researchers who discovered the bees.

So it must have been a land connection — presumably the Panama isthmus — that allowed for this migration, he said. (The findings appear in the journal Systematic Entomology.)

Most researchers believe that the Panama land bridge arose about three million years ago from tectonic and volcanic activity, connecting Central America to South America.

But Dr. Roubik and his colleagues believe the ancestors of the new bees originated in the Amazon about 22 million years ago and moved north into Central America about 17 million years ago.

The bees, as well as other fossil findings, indicate that there must have been an earlier land connection, Dr. Roubik said. And that connection is millions of years older than previously thought.

“There was an earlier chunk of land that linked Colombia to Costa Rica,” he said. “These are signs of a very old connection.”