Geographic Variation Of Egg's Effective Accumulated Temperature In Univoltine Populations And Effects Of Temperature On Diapause Termination Of Oxy A Chinensis

To investigate the strategy of the overwintering egg in Oxya chinensis Thunberg, incidence of embryonic diapause, diapause intensity, threshold temperature, effective temperature and the influence of low temperature on diapause termination were compared among four univoltine populations collected from Tieling, Jinan, Kaifeng and Xinyang cities. The main results are as followed:(1) The percentages of diapause of four populations were100%when eggs incubated at25℃. A part of eggs of Tieling and Jinan populations were hatched, but no eggs of Kaifeng and Xinyang populations were hatched during an observation period of100days. The first hatching occured on day61and78for the Jinan and Tieling pupulations respecitively.(2) The intensity of egg diapause was lowest in the Tieling population with a highest latitude, followed by the Kaifeng and Jinan populations with intermediate latitude, and highest in Xinyang population with a lowest latitudes. The results indicated that diapause intensity increase with the decrease of latitude.(3) The development period of O. chinensis decreased with the increase of incubation temperature, but there was a geographical variation among these four populations. The developmental threshold temperature and effective accumulated temperature of the four populations were analyzed by the least square method. The developmental threshold temperature were14.1±0.5℃,15.8±0.5℃,14.9±0.6℃,15.1±0.9℃and the effective accumulated temperature were179.1±8.6,187.8±10.1,197.7±10.2,208.2±8.9day degree for Tieling, Jinan, Kaifeng and Xinyang populations respectively. The results indicated that the developmental threshold temperature and effective accumulated temperature increased with the decrease of latitude.(4) Low temperature between0℃and developmental threshold temperature had strong effect on diapause termination and the longer of the time of low-temperature treatment, the more obvious of its effect on diapause termination. Hatching rate was the highest in the Tieling population and the lowest in Xinyang population. The suitable temperature ranged from1℃to13℃for Tieling population,4℃to13℃ for Jinan and Kaifeng populations, and7℃to13℃for Xinyang population, and the optimum temperature for diapause development was10℃for Tieling population,10℃for Jinan and Kaifeng populations, and13℃for Xinyang population.(5) Low temperature under0℃showed obvious influence on diapause termination rate of these four populations, but the influence showed obvious geographical variation among them. Low temperature under0℃didn't show obvious influence on the hatching rate of diapausing eggs in Jinan, Kaifeng and Xinyang populations, but the hatching rate of Tieling population could be obviously enhanced. The hatching rate of Tieling population was different when exposed to different temperature, and low temperature (-3℃) had the most strong effect on diapause termination.