Seasonal changes in supercooling point and cold tolerance in field collected larvae of the beet moth, Scrobipalpa ocellatella (Lepidoptera: Gelechiidae) in Karaj, Iran

A part of population of the beet moth, Scrobipalpa ocellatella (Boyd) in severe winter condition overwinters as larvae. In order to study overwintering potential ofthe pest, last instar larvae were collected monthly from September 2011 to March 2012. Seasonal changes in cold hardiness indices such as supercooling point (SCP) and lower lethal temperature of the beet moth were studied. The mean supercooling points of field collected larvae varied from –15.0 ± 0.99 to –17.8 ± 0.92 °C. Samples collected in October exhibited about 50% mortality, after 24 h exposure to -12 °C. It was gradually decrease until January (no mortality was observed) in January. Lethal temperature for 50% mortality (LT50) decreased from -13.2 ºC in October to -16.4 ºC in January. Supercooling points of overwintering larvae thorough the winter did not change significantly; while during the gradual decrease in ambient temperature, cold tolerance of S. ocellatella is progressively increased.