| The Asian corn borer (ACB) Ostrinia furnacalis (Guenée) is a major insect pest of corn in China. It overwinters as diapausing larvae. The cold-hardiness of diapausing larvae plays an important role in the survival of overwintering larvae, which will directly affect the population density of the first generation next year. Four geographical populations of ACB from Nong'an, Hengshui, Guangdong, and Hainan were reared in the laboratory using artificial diet at eleven different photoperiods and in 3 different temperatures combinations, to test how the two external factors affect diapause of ACB. The cold hardiness of diapausing larvae of 4 field populations from Jilin, i.e. Dunhua univoltine (DH1), Gongzhuling univoltine (GZL1), Gongzhuling bivoltine (GZL2), and Taonan bivoltine (TN2), were measured by exposing testing their supercooling point (SCP) and freezing point (FP). The cold tolerance were measured by testing the survival of diapausing larvae at supercooled. The proteomic approach was used to examine the proteins associated with diapause of ACB larvae.The results indicated that both of photoperiod and temperature were significantly impact on the diapause of ACB. It was showed that ACB performed a long-day response (long-day inducing growth) at 20℃. The critical photoperiods were 14h3min, 13h59min, 13h32min, and 13h7min for Nong'an, Hengshui, Guangzhou, and Hainan populations at 20℃. However, it was showed as shot-day-long-day response at 20℃. The highest diapause rate of 4 geographic population were 52.9%, 68.4%, 50.6% and 57.4% at 27℃for Nong'an, Hengshui, Guangzhou, and Hainan populations, which were significantly lower than that at 20℃. This indicates that the temperature could inhibit the diapauses of ACB. Their the critical photoperiod were 12h50min-13h32min, 11h36min-13h8min, 12h58min-13h6min and 11h50min-12h26min for Nong'an, Hengshui, Guangzhou, and Hainan populations, respectively, at 27℃.In addition, the diapause rate was much lower at 30℃than that at 20 and 27℃under the same photoperiod, this can be further verified that the temperature could weaken the diapauses rate of ACB. The results showed that the SCPs of ACB were varied from -28.5℃～-27.0℃, the lowest individual could be as low as -36.4℃.There were significantly differences in SCPs among the populations. GZL1 performed the lowest SCP and GZL2 the highest. There were 45.6, 58.8, 41.8, and 58.3% survival of diapausing larvae at supercooled to low sub-zero temperature -40℃for GZL1, TN2, DH1, and GZL2 populations, respectively. It was not significantly in post-diapausing development of these survivals compared with their non-supercooled original population. These results suggested that ACB diapausing larvae have extensive supercooling as well as freeze tolerance. It was concluded that the Asian corn borer may perform two strategies for survival at low temperature in diapause overwintering larvae of Asian corn borer, i.e. freeze tolerance and chill tolerance.There were 645±17 and 660±34 spots with molecular masses from 10-250 kDa detected in both diapausing and non-diapauseing ACB larvae protein with 2DE-saperation using Coomassie stain. Aout 190 protein spots were 5×or more differences in abundance between diapause and non-diapuase. Among them, 20 spots were diapause-unique, 89 upregulated, and 101 donwregulated. Arginine kinase was the only protein identified among the diapause-unique proteins, the others were unknown proteins.
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