Factors related to sound production by the Chinese grasshopper Acrida cinerea during escape

Many grasshopper species produce conspicuous sounds while escaping from approaching predators; however, they occasionally escape without producing sounds. The Chinese grasshopper, Acrida cinerea, often exhibits noisy escape behavior. Therefore, a field experiment was conducted using A. cinerea to identify factors related to the production of sound during escape. This study utilized a predator model with an investigator approaching A. cinerea three times. We examined the relationship between the production of sound during escape and the following factors: ambient temperature and relative humidity as environmental factors; sex, body length, body weight, and limb autotomy as prey traits; and the repeated approach as a predator trait. The relationships between noisy escape and flight initiation distance (i.e., predator-prey distance when the prey initiates the escape), distance fled (i.e., distance the prey covered during the escape), and the mode of locomotion during escape (i.e., flying or jumping) were also examined. Noisy escape was observed only in males that escaped by flying, whereas the females and males that escaped by jumping invariably escaped silently. Among males that flew, noisy escape was related to ambient temperature, limb autotomy, and distance fled. The proportion that produced sound increased in parallel with the ambient temperature and distance fled. This proportion was lower among individuals that had autotomized one of their hind legs. These results indicate that noisy escape behavior is most frequent in healthy male A. cinerea under warm conditions.