2 Millennia Of Locusts

One of the world’s oldest civilizations has now produced one of the longest-term looks at how climate influences insect populations. Drawing on more than 8,000 historical documents, researchers have assembled a 1,910-year-long history of the links between temperature, rainfall and outbreaks of locust swarms.

“Outbreak of Oriental migratory locusts (Locusta migratoria manilensis) was, together with drought and flood, considered one of the three most severe natural disasters causing damage to crop production in ancient China,” a team led by Huidong Tian of the Chinese Academy of Sciences in Beijing notes in the Proceedings of the National Academy of Sciences. “The earliest known written record of locusts was found inscribed on an ox bone in Oracle Script (Jiaguwen, the earliest Chinese script) 3,500 years ago, asking: ‘Will locusts appear in the field; will it not rain?’” Ever since, local histories and government documents have been littered with detailed records of locust outbreaks.

Other researchers have drawn on these records to examine links between the locusts and climate, but the results were often contradictory. In a bid to resolve the conflicts, the researchers compiled their unprecedented record, covering nearly 2 millennia. Although the records have gaps and inconsistencies, and vary over time, the team was able to extract some statistically significant trends.

For example, the team found that at both annual (A.D. 1512–1911) and decadal (A.D. 1000–1900) time scales, there was a strong link between locust populations and precipitation. “There were more locusts under dry and cold conditions and when locust abundance was high in the preceding year or decade,” they write. “This locust–precipitation correlation was found to hold at least as far back as to A.D. 500.”

The link between temperature and locust outbreaks “was weaker and less consistent,” they note. That suggests “temperature may affect locusts in an indirect way, as cooling decreases summer monsoon rainfall through reduced moisture transport from the surrounding oceans to the Asian continent.”

“In general, studies on climate change based on long-term biological data are extremely rare,” the team notes. But they anticipate that, “as more and better proxies of the historical fluctuations in climate are becoming available to the scientific community,” other researchers will want to take a fresh look at their extensive “locust index.” It provides a “unique opportunity,” they note, to gain insight “into biological consequences of global climate change in the years to
come.”David Malakoff | August 30, 2011

Source: Tian, H., Stige, L., Cazelles, B., Kausrud, K., Svarverud, R., Stenseth, N., & Zhang, Z. (2011). Reconstruction of a 1,910-y-long locust series reveals consistent associations with climate fluctuations in China. Proceedings of the National Academy of Sciences, 108 (35), 14521-14526 DOI: 10.1073/pnas.1100189108

Image © Dohnal | Dreamstime.com