I have this dwarf orange tree in my yard (SF bay area in CA). Last year during the summer and recently this year I noticed that at the very top of the plant (end of highest branches) there was a cluster of small black bugs and they were being tended to by a stream of ants (they did not look like ant larve).
What are these bugs?
Do I need to get rid of them vigorously? (they don't seem to be causing much plant stress)
Are they aphids (they look larger and blacker than what I thought)? Do I remove the effected leaves to evict the bugs or do I control the ants?