Computer tomography-assisted visualization of the movement triggered by frost in Ostrinia nubilalis overwintering in maize stalks

The damage of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), causes is mainly determined by the success of its overwintering. The aim of our study was to assess the consequences of the artificial cooling on the movement and survival ability of overwintering larvae of O. nubilalis by using computer-assisted tomography. The in situ movement of the examined larvae in icy media of different thickness (5, 15, and 30 cm) and during freezing periods of 5, 10, 20, 40, and 60 min was determined in maize stalks using CT and the positioner-laser of the CT apparatus. It has been found that the thickness of the ice had a significant effect on the displacement of the overwintering larvae, however, the impact of the duration of freezing on the moving of the larvae could not be proven statistically. Enhanced larvae activity due to thinner ice layers (5, 15 cm) were of exponential type, which was more pronounced just prior to the freezing point. In contrast, thicker ice covering (30 cm) caused complete immobility. According to our results, the diapausing larvae were still able to move and albeit it appeared to be capable of surviving the direct impact of extreme cold, it could even leave its overwintering place as a result of low temperature. Furthermore, the maize stalk tissue contributes to the survival-success of the larvae as it seems to act as a temperature-buffer moderating the severe impact that low temperature exerts on living tissue.