I have an idea for yet another "bio-weapon". It will be a virus that spreads normally. However, when a bot infected with this virus gets hit by the same virus again, it dies. This can start a chain reaction in dense colonies of robots. The infected bots will fire the virus at other infected bots, which will die. This could be used as a form of crowd control. This is only a suggestion, though. I just thought it was a neat idea.