If you were going to kill some ants...

[penumbra]

Leave it fully submerged into water for a couple of hours, like 2 or 3 and then leave it on top of a bowl of water or something like that for a few days. They'll be gone for a while for sure.

Do this^^^

Check WHY they are on your tree. For sure you will find scale, aphids or the likes on the tree. A bonsai is NOT interesting for ants in itself.

Look for this^^^

It has some small white patches of a cotton-like substance scattered intermittently on the trunk and branches.

You found the cause^^^

I would go with an imidacloprid systemic. Care must be taken to remove flowers if the tree is blooming as this insecticide is very harmful to bees.

Most effective^^^

 

[Srt8madness]

I hope the OP solved the problem in the 3.5 years between their post and today's replies

 

[penumbra]

Damn ............
thought this all sounded familiar. Let sleeping dogs lie.

 

[yashu]

That’s what happens when you look at “Similar Threads” thinking it’s the “current threads”