Cold-hardiness of diapausing corn borer larvae is correlated with the glycerol concentration. Larvae containing 5.7% glycerol are cold-hardy at -10, -22 and -35C whereas those containing 5.0% glycerol are cold-hardy only at -10 and -22C. The larvae containing 2.1% glycerol are not cold-hardy. Frozen cold-hardy borer larvae survive longer at -22C than super-cooled larvae. Intermittent chilling caused higher mortality than continuous chilling at -22C, presumably because larvae experienced frequent lethal freezing-thawing cycles during intermittent chilling. The protective function of snow layer on the winter survival of the borer larvae was investigated. Larvae moved from corn stalks which were under a snow cover had a survival 15% higher than those from the upper part of the stalk exposed to the air. The under-snow-level population may benefit from the constant and relatively warm surrounding environment provided by the snow layer. First appearance of borer moths and different cumulative levels of moth flight activity can be predicted by the use of five-year-moth-flight data and heat units. Five organic acids, citric, succinic, aconitic, malic and tartaric acid were analyzed by gas-liquid chromatography to determine whether different concentrations were present in cold-hardy and non-cold-hardy larvae. The concentration of organic acids in the haemolymph of cold-hardy and non-cold-hardy was similar. Organic acids do not appear to contribute to the development of cold-hardiness in the borer larvae.