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Grasshopper swarms take young researcher to China

November 12, 2010

They were the scourge of the ancient world. For centuries, locust outbreaks have been associated with the loss of crops, destruction and famine. The hunger of these creatures is voracious – there’s even tales of locusts eating people’s clothes.

Curiously, some species of locusts are solitary, but others congregate into ravenous swarms. What exactly triggers these insects to form swarms and why?

For the past three years,  Arianne Cease, doctoral candidate in the School of Life Sciences (SOLS), has been travelling to the northeastern grasslands of China to understand the behaviors of Oedaleus asiaticus (a dominant species of locust common to the region), including the effects swarms have on the environment.

“It is one of just 20 to 30 species of grasshoppers worldwide that have the capability of gathering and creating a migratory swarm,” Cease said. “But in order to do this, the grasshopper as a juvenile must be exposed to certain environmental stimuli.”

For example, grasshoppers must grow in a sociable way, surrounded by other grasshoppers and locusts in order to develop a migratory phenotype (traits an organism develops based on genetics and environmental factors). In the case of the sociable grasshoppers, they develop strong flight muscles and exhibit increased wing area – traits that are useful in a migratory swarm.

According to Cease, the crowding exposure also changes the behavior of most locust species, and as adults tend to group rather than remain solitary.

Another factor Cease and her colleagues examined was the morphology of Oedaleus asiaticus and tried to determine if coloration had any connection to their behaviors.

“Anecdotally we know that swarms are associated to the brown phenotype, not the green ones,” Cease said. “We found out that the brown ones do have bigger flight muscles and bigger wings.”

But the most astonishing aspect of the research the ASU team has made in China is that the locusts are eating nutrient deprived grasses – literally, the leftovers that grazing animals leave behind.

“There’s been a lot of steppe degradation, it’s mostly caused by livestock overgrazing. The interesting link is that [these grasshoppers] thrive in poor quality areas,” Cease said. “So you have an overgrazed area and then get the grasshopper outbreak that comes on top of it and further degrades the specific grassland.”

This research has brought exceptional SOLS undergraduate researchers to the field in Inner Mongolia. Colleen Ford (2009) and Jennifer Esman (2010) spent two months of their summer working closely with Cease and collaborators in China as part of Research Experience for Undergraduates (REU) grants through the National Science Foundation (NSF).

The findings of the ASU team of Arianne Cease, James Elser, Colleen Ford and Jon Harrison, in collaboration with professors Shuguang Hao and Le Kang of the Chinese Academy of Sciences, were published in the August edition of the Journal of Insect Physiology.