Protein-rich diets can be detrimental to the locust species Oedaleus asiaticus, according to researchers working in northeast China. As a consequence, swarms of these locusts are more likely to occur where vegetation contains low levels of nitrogen—a primary protein source for the insects.
Unfortunately for many farmers, erosion and heavy grazing by livestock contribute to desertification—a significant problem in China—but also reduce the amount of nitrogen in crops, thereby increasing the chances of a locust swarm on overgrazed land.
Arianne Cease from Arizona State University in Tempe, Arizona, and colleagues from Beijing, China, studied this particular species of locust, which is a major pest on the north Asian grasslands, and found that high-nitrogen diets decreased both the size and viability of the insects. Their report appears in the 27 January issue of the journal Science.
A juvenile locust with dishes of dried/ground Stipa grandis — their favorite plant. The dish on the left contains low-nitrogen plants collected from a field heavily grazed by livestock. The dish on the right contains the same plant, but collected from an ungrazed field. | Photo courtesy of Arianne Cease; © Science/AAAS
The locusts “are currently the target of pest control research at several agricultural universities in Inner Mongolia, as well as the Institute of Zoology at the Chinese Academy of Sciences in Beijing, where our collaborators are located,” said Cease. “Outbreaks are common near rural villages where people depend on livestock for their livelihood. When outbreaks are at high enough densities, they can travel some distance and attack other ranges and croplands.”
Cease and her colleagues knew that all living organisms aim for optimal diets that provide them with just the right amount of protein. But they weren’t sure how sub-optimal diets might affect various species in the wild. To determine this, they performed detailed experiments in the field and in the laboratory to gauge the effects of several grasses—each with different levels of nitrogen—on the locusts’ diet.
The researchers found that the locusts prefer eating plants with low nitrogen levels and, when given the choice, diets with low protein and high carbohydrate levels.
A locust in its preferred habitat, a field heavily grazed by sheep (background) near the Inner Mongolia Grassland Ecological Research Station in northeast China. | Image courtesy of Arianne Cease; © Science/AAAS
“When we fed these locusts high-protein grass, they tended to die more frequently than when confined to low-protein grass,” said Cease. “When we gave them a choice, they selected the grass with the lowest protein content.”
According to the researchers, plant nitrogen levels were lowest and locust abundance was highest in the heavily grazed fields near the Inner Mongolia Grassland Ecological Research Station in northeast China, where the soils had been depleted of nitrogen.
These findings imply that nitrogen-rich fertilizers may be useful as an alternative pest control for this particular species of locust. And they might inform some land- management decisions as well, according to Cease.
“We already knew that overgrazing was a problem that can lead to desertification,” she said. “This study provides us with a new understanding of how the overuse of grasslands can cause locust outbreaks and destruction, not only in the local area but in surrounding agriculture as well.
“Working together with scientists from other fields, land managers, policymakers and other stakeholder groups, we can create innovative management strategies to both limit land degradation and maximize ecosystem function for the benefit of communities who depend on the land.”
26 January 2012
Read the abstract, “Heavy Livestock Grazing Promotes Locust Outbreaks by Lowering Plant Nitrogen Content,” by Arianne Cease and colleagues.
Listen to a Science Podcast interview with Arianne Cease.