Looks like the ants have things sewn up. The green aphids (hardly visable to the naked eye) seem to be atrracted to the white stuff the ants are secreting, which then sticks to them and effectively traps them...for the ants to eat later, I assume?
On the apple tree in the garden. Macro lens, tripod and remote release - tried to do macro properly for a change! View LARGE...let me know if you feel itchy!