[BEIJING] A surprising finding promises a cheap and environmentally friendly way of controlling locust swarms, a major plague that devastates crops around the world.
Land erosion caused by heavy livestock grazing promotes locust swarms by lowering the nitrogen content in plants that locusts feed on, according to a study published in Science today (27 January).
Conversely, the study also found that locusts do not thrive on nitrogen-rich food, as previously thought, but are in fact hampered by it.
"Nitrogen fertiliser — which plants use to make protein — may be an inexpensive, more environmentally friendly pest control solution for this species," said the lead author Arianne Cease, a researcher at Arizona State University, United States.
Most herbivores, including insects, are thought to be limited by the availability of nitrogen-rich protein in their diets.
But scientists were surprised to find that this is not the case for Oedaleus asiaticus, a dominant locust of the north Asian grasslands and a close relative of the common African pest O. senegalensis.
The Chinese–US team studied the locusts at the Inner Mongolia Grassland Ecosystem Research Station, part of the Chinese Academy of Sciences (CAS).
Field observations found that locusts were less likely to survive in fields that were fertilised with nitrogen, and their density was highest in the most heavily grazed fields — which were dominated by plants with low nitrogen content. Laboratory experiments showed that locusts preferred to eat plants with low nitrogen content.
"This is the first time it has been shown that Oedaleus locusts strongly prefer to consume low- nitrogen plants from heavily grazed plots," Kang Le, a locust expert at CAS's Institute of Zoology and a co-author of the study, told SciDev.Net.
Since heavy livestock grazing in Mongolia leads to a loss of topsoil and nitrogen, this also means that overgrazing may promote locusts outbreaks, according to the study. "With enhanced soil erosion, locust swarms could become more common," Cease said.
The habitat studied by the researchers is typical of the Eurasian grasslands that cover much of Afghanistan, Bhutan, China, Iran, Nepal, Pakistan, and some of northern India. But researchers say that their findings might also apply in other regions with locust swarms.
"We suspect that something similar might be happening in closely related species," Cease added. "For example, the Senegalese grasshopper (Oedaleus senegalensis) shares the same genus as our Asian species. It is … considered the main pest of the Sahel, voraciously targeting millet and sorghum fields.
"We have applied for funding to collaborate with researchers in Senegal," Ceasse said. "Our goal is to understand if what we have learned about the Asian locust can be applied to other locusts and be used to help minimize outbreaks in the Sahel."
Tong-Xian Liu, professor of entomology, and dean of the College of Plant Protection at Northwest A&F University, in China, said the study will have "a revolutionary impact" on the way we think about locust pest management and grazing practices.
Science 335, 467–469 (2012)