By April 1960, Chinese leaders changed their opinion due to the influence of ornithologist Tso-hsin Cheng[2] who pointed out that sparrows ate a large number of insects, as well as grains.[8][9] Rather than being increased, rice yields after the campaign were substantially decreased.[10][9] Mao ordered the end of the campaign against sparrows, replacing them with bed bugs, as the extermination of the former upset the ecological balance, and bugs destroyed crops as a result of the absence of natural predators. By this time, however, it was too late. With no sparrows to eat them, locust populations ballooned, swarming the country and compounding the ecological problems already caused by the Great Leap Forward, including widespread deforestation and misuse of poisons and pesticides.[10] Ecological imbalance is credited with exacerbating the Great Chinese Famine, in which 20–45 million people died of starvation.[11][12]
https://en.wikipedia.org/wiki/Four_Pests_Campaign
By April 1960, Chinese leaders changed their opinion due to the influence of ornithologist Tso-hsin Cheng[2] who pointed out that sparrows ate a large number of insects, as well as grains.[8][9] Rather than being increased, rice yields after the campaign were substantially decreased.[10][9] Mao ordered the end of the campaign against sparrows, replacing them with bed bugs, as the extermination of the former upset the ecological balance, and bugs destroyed crops as a result of the absence of natural predators. By this time, however, it was too late. With no sparrows to eat them, locust populations ballooned, swarming the country and compounding the ecological problems already caused by the Great Leap Forward, including widespread deforestation and misuse of poisons and pesticides.[10] Ecological imbalance is credited with exacerbating the Great Chinese Famine, in which 20–45 million people died of starvation.[11][12]