How about to place a new Topic from time to time in News section with a text like this.
"Hey Folks, this is a thread to prevent bots and spam. All you have to do is to write something here, which is not totally sensless or something like "Thanks for the News", "Good News", "Thanks", "Nice".
What happens if you still do this? You get banned from here, how simple is that? So you dear Spammers and Bots enjoy your Ban and try it again starting with Lvl. 0."
Maybe with changing Headlines, to see who really read "The News" and who is just spamming. And Ban those who are replying to this thread with one of those phrases
edit: Thanks to the Mods to listen to my Suggestion and doing it https://eu.alienwarearena.com/ucf/show/1780828/boards/gaming-news/News/a-new-game-called-bot-trap