Variation of supercooling point in overwintering larvae of Scrobipalpa ocellatella (Lepidoptera: Gelechiidae)

The beet moth, Scrobipalpa ocellatella (Boyd) (Lepidoptera: Gelechiidae) is one of the most destructive pests of beet. The insect overwinters as larvae of different instars in beets which are left in the field. Supercooling point (SCP) of individual larvae showed broad range variation from -۶ to -۲۵ °C. In the present study, factors affecting the broad range of SCP were investigated. Larvae showed a great increase in SCP when they were induced by exogenous ice nucleation. Defensive oral discharge (DOD) decreased SCP but it had no significant effect on supercooling ability of larvae. The presence of sufficient food in guts of field collected larvae induced an increase in SCP. Therefore it could be concluded that surface moisture and food particles in the gut may act as ice nucleating agents (INAs) that cause freezing of the body fluids at higher temperatures. Furthermore, second and third instar larvae, owing to their small size, had greater capacity to supercool in comparison to fifth feeding instars. Broad range in SCPs might be due to diversity in overwintering larvae which have different capacity for supercooling.