Cold tolerance of field-collected and laboratory reared larvae of Sesamia nonagrioides (Lepidoptera: Noctuidae).

Sesamia nonagrioides Lefébvre (Lepidoptera: Noctuidae) is considered one of the most destructive pests of corn in the Mediterranean region. The purpose of the present study was to investigate some aspects of the cold tolerance of non-diapausing and diapausing laboratory reared larvae of S. nonagrioides, as well as of field-collected larvae, taking into consideration various parameters, such as supercooling ability, mean lethal temperature and accumulation of cryoprotectant substances, in relation to diapause. Our results provide evidence that S. nonagrioides has limited cold tolerance as it displays a low ability of supercooling. This is strongly supported by the fact that mortality of the individuals occurred after extended exposure to subzero temperatures, equivalent or slightly lower to their mean supercooling point. However, lethal temperatures of diapausing larvae were significantly lower in relation to that of non-diapausing larvae, indicating the existence of a direct link between diapause and cold tolerance. Regarding the role of cryoprotectant substances, accumulation of glycerol seems to be closely related to diapause, in contrast to accumulation of trehalose, which is more related to exposure to low temperatures slightly higher than 0 degree C. Finally, non-diapausing larvae of different instars displayed a similar ability of supercooling and tolerance to low temperatures as well as accumulation of cryoprotectant substances. The ecological significance of our findings on cold tolerance of this species is being discussed with particular reference to the microclimate observed in northern Greece.