I built such bumblebee houses a few years ago with the kids. The flap is essential against a kind of flies that lay their eggs in the bumblebee nest and their caterpillars eats the nest.
Either the Queen or the others learn the usage quite fast. Sometimes next generation queens remember it in the next year
No, the next generation queens grow in that swarm and learn it there. All swarm members learn it. To the queen (or the first few workers) you teach it. The rest learns from the others. But the workers are short living (few weeks). The queens live for about a year and can take knowledge in the next year.
