False codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae) larvae are chill-susceptible

This study reports on the low temperature tolerance and cold hardiness of larvae of false codling moth, Thaumatotibia leucotreta. We found that larvae have mean critical thermal minima (lower limits of activity) of 6.7 degrees C which was influenced by feeding status. The effects of low temperature exposure and duration of exposure on larval survival were assessed and showed that the temperature at which 50% of the population survives is -11.5 +/- 0.3 degrees C after 2 h exposure. The supercooling point (SCP, i.e., freezing temperature) was investigated using a range of cooling rates and under different conditions (feeding and hydration status) and using inoculative freezing treatments (in contact with water or orange juice). The SCP decreased significantly from -15.6 degrees C to -17.4 degrees C after larvae were fasted for 24 h. Twenty-four hour treatments at either high or low relative humidity (95.9% or 2.4%) also significantly decreased SCP to -17.2 degrees C and -18.2 degrees C respectively. Inoculative freezing (by water contact) raised SCP from -15.6 degrees C to -6.8 degrees C which could have important implications for post-harvest sterilization. Cooling rates did not affect SCP which suggests that there is limited phenotypic plasticity of SCP during the larval life-stage, at least over the short time-scales investigated here. In conclusion, larvae of T. leucotreta are chill-susceptible and die upon freezing. These results are important in understanding this pest's response to temperature variation, understanding pest risk status and improving post-harvest sterilization efficacy.