Age-dependent changes in tolerance to cold and accumulation of cryoprotectants in overwintering and non-overwintering larvae of European corn borer Ostrinia nubilalis

The age-dependent cold hardiness profile of Ostrinia nubilalis is compared between nondiapausing and diapausing larvae, as well as with field-collected larvae. The results suggest that both cold tolerance and accumulation of cryoprotectants depends upon the age of O. nubilalis larva. Late fifth-instar nondiapausing larvae are more cold tolerant than younger fifth-instars because they show enhanced ability to withstand sub-zero temperatures. No appreciable difference is observed between the experimental groups of diapausing larvae as far as their supercooling ability and tolerance at sub-zero temperatures above the supercooling point. In general, both field-collected and diapausing larvae are more cold tolerant than nondiapausing larvae, indicating a direct link between diapause and cold hardiness. The age of diapausing larvae affects the ability to accumulate glycerol. Glycerol levels of 45-day-old diapausing larvae are significantly higher (2.7-fold) compared with 90-day-old diapausing larvae. Moreover, diapausing larvae display a five- to 13-fold higher glycerol content compared with nondiapausing larvae. There is a trend for an age-dependent cold hardiness profile in O. nubilalis and further tests that could demonstrate a causal relationship between age and cold tolerance are needed.