Cold hardiness strategy in field collected larvae of Scrobipalpa ocellatella (Lepidoptera: Gelechiidae)

The beet moth, Scrobipalpa ocellatella is recognized as a widespread agricultural pest. Cold hardiness strategy of the beet moth larvae was investigated through monitoring seasonal changes at supercooling points and lower lethal temperatures. Furthermore, the role of microhabitat in winter survival was studied. The mean SCPs of the last instar larvae was not significantly different from November 2010 to April 2011. Mean inoculative freezing point (8.0 ± 1.44 °C) of the last instar larvae was significantly higher than mean SCP (14.9 ± 0.93 °C). The cold hardiness of the pest shows seasonal fluctuation in response to reduction of air temperature. A 50% mortality (LT50) occurred at 11 ºC in November and 14 ºC in January and reduced to 18 ºC in February and finally increased to 14.5 ºC in April. Glycerol, sorbitol, trehalose, and myoinositol were identified components in whole body extracts of S. ocellatella larvae. However, total cryoprotectants could not have significant effects on the cold tolerance. Larvae of S. ocellatella could tolerate subzero temperatures near their SCPs. Our findings show that beet moth larvae utilize moderately chill tolerance strategy during winter.