Seasonal and geographical variation in diapause and cold hardiness of the Asian corn borer, Ostrinia furnacalis.

Asian corn borer, Ostrinia furnacalis (Guenée), is a key corn pest in the Asian-Western Pacific countries. Supercooling point (SCP) and survival rate after low sub-zero temperature treatment were assessed using a cool bath with a 1°C/min cooling rate until −40°C for field-collected populations from several locations ranging from northeast to southern China. Mean SCPs were varied among geographical populations with a significant decline from −22.7°C for a multivoltine tropical population in the south to −28.5°C for a univoltine temperate population in the northeast.  In addition, there was more than 1°C difference in SCP between univoltine and bivoltine populations that were from the same location (Gongzhuling). Over 41% of overwintering larvae from the northeast population could withstand to be supercooled briefly to the low sub-zero temperature of −40°C, but only 6.7% of their southern counterparts did so. The findings from this study suggest that O. furnacalis mostly takes advantage of freeze avoidance as diapausing larvae for overwintering in the southern region, whereas it exhibits freeze tolerance in diapause in the northeastern region.