Effects of JH and ecdysone on endogenous ice nucleus production in larvae of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Ice nucleus production of larvae of the rice stem borer, Chile suppressalis Walker has been observed to be related to diapause and cold temperature exposure. To determine the effects of insect hormones that regulate larval diapause on ice nucleus production, non-diapausing mature and overwintering (diapausing) larvae were treated with juvenile hormone (JH) and ecdysone. When JH-I was applied, the crystallization temperature of the muscle and epidermis rose in non-diapausing mature larvae, but not in overwintering larvae, which might contain highly endogenous JH. However, injection of 20-hydroxyecdysone lowered the crystallization temperature in overwintering larvae. These results show that ice nuclei in the muscle and epidermis are activated by JH and inactivated by ecdysone.