Variation of embryonic diapause intensity and life-cycle pattern in five geographic populations of the Chinese rice grasshopper,Oxya chinensis(Orthoptera:Acridoidea:Catantopidae) from China

To investigate the geographic adaptation of the grasshopper,Oxya chinensis,populations of this grasshopper were collected in 5 localities ranging from 42.3°N to 20.0°N in China,and incidence of embryonic diapause,diapause intensity and adult body size were compared among the populations using their offsprings.The results indicated that different populations of the grasshopper displayed different patterns of response to photoperiod and temperature.The incidence of diapause was not influenced either by photoperiod or temperature in Tieling,Jining and Sihong populations,and their diapause rate was 100% under any conditions.Partial eggs entered diapause in the southern populations,i.e.Changsha and Haikou populations.A higher proportion of diapause eggs were produced at a short photoperiod than at a long photoperiod and the incubation temperature greatly influenced the induction of diapause in Haikou population,whereas the incidence of diapause in Changsha populations was only regulated by the incubation temperature of eggs.The egg diapause intensity was lowest in the Changsha and Haikou populations, followed by the Tieling population,and highest in the intermediate latitude populations,i.e.Jining and Sihong populations.In addition,diapause intensity increased as the original latitude decreased within the northern univoltine area.Adult body size showed a complicated pattern of variation along the latitudinal gradient.Significantly negative correlations between body size and latitude occurred within the northern populations;the body size of Changsha and Haikou populations,however,was smaller than that of Jining and Sihong populations.These results suggest that O.chinensis geographic populations have developed locality-specific adaptations,and the latitudinal gradient appears to play an important role in shaping their life-cycle and development.