Entomological warfare (EW) is a type of biological warfare that uses insects to interrupt supply lines by damaging crops, or to directly harm enemy combatants and civilian populations. There have been several programs which have attempted to institute this methodology; however, there has been limited application of entomological warfare against military or civilian targets, Japan being the only state known to have verifiably implemented the method against another state, namely the Chinese during World War II. However, EW was used more widely in antiquity, in order to repel sieges or cause economic harm to states. Research into EW was conducted during both World War II and the Cold War by numerous states such as the Soviet Union, United States, Germany and Canada. There have also been suggestions that it could be implemented by non-state actors in a form of bioterrorism. Under the Biological and Toxic Weapons Convention of 1972, use of insects to administer agents or toxins for hostile purposes is deemed to be against international law.