It has been known that Apis cerana (Asian hive bee) drones will congregate
on an orchid (originally from China but widely planted in Japan). I believe
I have seen pictures of only drones on the flowers, although some has
workers also. Apparently the flower produce chemicals similar to queen
pheromones and attract drones (who try to mate with the flowers and in the
process pollinate the plant).

so my hypothesis is that there are some queen pheromone left on the branch
(since a swarm landed before), and this place is close to a drone
congregation area. so drones got attracted to the pheromone (they apparently
only become attracted while flying in congregation areas -- e.g. they ignore
the pheromone while in hive).

Zach
http://www.beetography.com

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