The simplest solution for ants kills all of them effectively but does not use pesticide. You will need laundry borax, sugar, and some sort of disposable small plastic container with a lid.
(Important: borax is not a pesticide but is toxic, which is why this works. Don't use in any situation where a pet or child might ingest the bait)
Take your small container with lid, around the lip of the container, with scissors, clip holes that are about a half cm, do this in 4 or so locations. These allow ants into the trap.
Place the lid up side down.
Mix one part laundry borax with 3 parts sugar. You can make a quantity of this, but store in a container clearly labeled with something like "borax ant killer".
Take a half teaspoon of the mix, place it in the center of the up side down lid. Moisten the mix with just a few drops of water (enough to just wet the mix).
Put the container (with holes clipped around the edge) up side down on the lid. Place this with the lid down any place you see ants walking.
You will initially see more ants drawn to the bait, and think something has gone wrong. After a few hours, ants will decrease. After one or two days, no more ants.
When the ants are gone, wash off the trap, store with your borax mix for the next time.