ants like to set-up home in pots which is a problem as their network of tunnels creates rapid drainage leading to root dryness also maples have sweet sap which attracts ants plus they milk greenfly for their honeydew.

Where are you keeping your bonsais? Mine are up off the ground on sort-of slatted shelving, so luckily I don't have the ant problem. If you can put them in dishes it might help.

Check the plants for aphid infestation - this is usually the reason why ants are on plants, they like the honeydew the aphids produce. If present, spray to kill the aphids.