The locust plagues in the Yangtze River Delta of China during the Ming and Qing Dynasties

The Little Ice Age was concurrent with frequent natural disasters in China during the Ming and Qing Dynasties (1368–1911 AD). Using historical documents created in the Yangtze River Delta during these dynasties, we reconstructed the severity and frequency of locust plagues. We uncovered their temporal and spatial patterns, the relevant influencing factors, and the applied control measures. These locust plagues occurred in the Yangtze River Delta during summer and autumn and were considered moderate-degree disasters. The locust plagues during the Qing Dynasty were less harmful than those during the Ming Dynasty. The locust plagues occurred north of 31°N and were concentrated around lakes and rivers. Regarding long-term changes, three periods of frequent locust plagues were identified: 1520–1540 AD, 1610–1670 AD, and 1850–1870 AD. The locust plague cycles were dominated by long-term changes of 100 and 350 years, alternating with short-term changes of 10–30 years. Locust growth and development typically occur under suitable climate conditions. However, in the Yangtze River Delta, the relationship between locust outbreaks and temperature changes was insignificant, whereas flood disasters provided suitable humidity conditions for locust nymph growth. Locust plague outbreaks had a series of social impacts, one direct result was rising food prices. When facing locust plagues, the Ming and Qing Dynasties formed effective top-down preventative measures corresponding to local conditions. The locust plagues in the Yangtze River Delta during the Ming and Qing Dynasties occurred with regularity, were responsive to local hydrological conditions, and impacted social economies and technologies.