Geographic variation in embryonic diapause, cold-hardiness and life cycles in the migratory locust Locusta migratoria (Orthoptera : Acrididae) in China

To investigate geographic adaptation of the migratory locust Locusta migratoria in China, locusts were collected from six localities, ranging from 47.4 degrees N to 19.2 degrees N. Using offspring from the various populations, we compared embryonic diapause, reproductive traits, cold-hardiness and adult body size. The incidence of embryonic diapause was influenced by the genetic makeup, parental photoperiod, and incubation temperature of the eggs. The northern strain (47.4 degrees N) produced diapause eggs under all photoperiodic conditions, whereas the other strains produced a higher proportion of diapause eggs when exposed to a short photoperiod. The incubation temperature greatly influenced diapause induction. At a low temperature, all eggs entered diapause, even some of those from a tropical strain (19.2 degrees N) in which no diapause was induced at high temperatures. Photoperiodic changes during the parental generation affected the incidence of embryonic diapause. Diapause intensity decreased with decreasing original latitude. Cold hardiness was compared by exposing eggs in diapause to either -10 or -20 degrees C for various periods; the northern strain was more cold-hardy than the southern strain, although some eggs in the tropical strain were probably not in a state of diapause. Adult body size and head width showed a complicated pattern of variation along the latitudinal gradient, whereas egg pod size (egg pod width and egg number) and hatchling weight tended to decrease with decreasing latitude. These results reveal that L. migratoria has adapted to local environments and that the latitudinal gradient appears to play an important role in shaping L. migratoria life cycle and development.