Ants hovering at base of crabapple tree

Horticulture
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I’ve owned this 60 year old crabapple tree for nearly 20 years. Discovered ants running up/down the main trunk to reach the new growth about a week ago. Closer inspection uncovered aphids on the leaves of the newest growth.

I cut out all new growth harboring aphids, hosed off remaining leaves, allowed tree to dry, then sprayed the entire tree (trunk, branches, leaves and soil) with Safer Insecticidal Soap. That was Monday.

Today the ants are back, hovering at the base of the trunk and moving in/out of the hollows. No aphids or other insects appear to be present. Could the ants have built a nest in the pot among the roots and soil?

Any suggestions for getting rid of the ants before they damage the tree (can’t repot til Spring)? A different/stronger spray? Another round of insecticidal soap?

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This is all based on my understanding. I’m new to bonsai but have been gardening for a good whole and have kept carnivorous plants for years.

It’s my understanding that ants don’t really attack the tree. They eat the honeydew that aphids and others leave behind. Ants will even protect plant suckers from other predators. From what I’ve read, experienced, and what you said my guesses at what’s happening and how to fix it would be:

  1. You probably sill have plant suckers on the tree. You may just not be able to see them. It’s unlikely that a single treatment took care of the issue. They may have fallen into the soil and their young are hard to see.
  2. If you did successfully get rid of them, the ants may have a colony in the substrate. They eat the honeydew plant suckers leave behind and will even protect them from predators. Your removal of the suckers may have left honeydew the ants are still collecting or the colony is hoping they come back for the food source. Deny them food and they may go away.
  3. Maybe it’s something else. Personally, I’d use bait traps to lure them to kill them if you want to get rid of them. A lot of the aphid/mite killing organic stuff won’t hurt ants since they are built differently.
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I’ve had similar problems with ants.
Tried submerging the pot, a few insecticides but what finally worked was adding ant killer granules in small quantities from time to time when they are most active.
They’ll eat them and feed it to the rest of the colony slowly wiping them out.

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You can also get ant nematodes which although they don’t kill the ants they cause an itch and eventually the ants move on.