Cold hardiness in the European corn borer, Pyrausta nubilalis (Hübn.)

Abstract

The relationships between undercooling capacity, tissue freezing, and survival at subzero temperatures were studied in mature larvae of the European corn borer, Pyrausta nubilalis (Hübn.). Undercooling temperatures were determined by means of a thermistor-thermometer. Larval survival was measured at −10, −15, and −20°C. It was found that the undercooling temperatures of the larvae were not a reliable indication of their ability to survive under subzero conditions. Cold-hardening of borer larvae in the field began in August and continued to increase until late November. Summer larvae in diapause succumbed rapidly to low temperatures. Cold-hardy winter larvae, on the other hand, survived up to 3 months at −20°C, when in the absence of contact moisture. Chilling in the presence of contact moisture caused freezing of the larvae and reduced their ability to survive cold conditions. Despite the formation of ice in their tissues, fully cold-hardy borers survived several weeks while frozen at −20°C. The undercooling temperatures of cold-susceptible larvae were lowered by chilling and desiccation, but such treatment did not significantly enhance their ability to survive subzero conditions. Cold hardiness was destroyed by incubating cold-hardy larvae at 30°C, either with or without contact moisture.