you should have taken action when you had seen one.... but it seems u r late...

anyway, so far as  i know boric acid helps....(but cannot confirm as I have not tried)...

better tell your landlord about it...(but don't tell them that your friend brought it from somewhere)... just tell him you yourself don;'t know where it came from... (well it depends upon how much your landlord is helpful...if he is strict....better not tell in this case.....may bring other problems )

but keep your rooms clean before u let him know