Does "Swarm" AI card affect all Locust on the map?
Yes it is part of the game mechanics to bring the distant locust back into the game. Most of the "For Each" Locust AI cards only move the figures one or two areas and only spawn Locust if there are no figures in play of the listed type. Rules of play book suggest that if there is no space to place the piece off the edge of the map.

With that said it could be possible to have Locust type A, B, and C at the far end of the map with minimal effects on the player from Locust AI card if there was no card like this.