aphids... brought in by ants. pour fine GD all over the ground and and even dust the tree, trunck too. or you can spray them off with water with a strong stream. or put on a poison.

Aphids don’t require ants in order to become a pest problem. At a certain time of year, female aphids are born with wings. These individuals can readily fly to other host plants and start bearing live young parthenogenetically. A few generations later, you have a big problem! No ants needed whatsoever.

I suggest that you use fairly strong sprays of water and/or your fingers to squish them before they can continue to multiply.