Before the 20th century, people and their cattle simply did not live in areas infested with tsetse flies. In the 20th century, using pesticides after World War II caused as many problems as it solved. Now more subtle methods are preferred. Tsetse flies can be trapped by using large blue cloths as a lure. Another good method is to release irradiated male flies, which are sterile. Since females mate only once in their lives, that much reduces the population.