Circulation

Effects of photoperiod, temperature and hormones on glycerol content and endogenous ice nucleus production in larvae of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Copyright

H. Tsumuki

Research Institute for Bioresources, Okayama Univ., Kurashiki 710-0046, Japan

Overwintering larvae of the rice stem borer, Chilo suppressalis, are freeze-tolerant (Tsumuki, 1990). Although overwintering larvae of this species produced high content of glycerol, the crystallization temperature was maintained at around –14 o C by the production of ice nuclei (Tsumuki and Konno, 1991; Hirai and Tsumuki, 1995). Since enhancement of insect low temperature tolerance is a seasonal phenomenon, photoperiod and low temperature may be responsible for the production of glycerol and ice nuclei. To determine the effects of photoperiod and temperature on the production of glycerol and ice nuclei, mature larvae reared at 25 o C under short (10L: 14D) and long (16L: 8D) photoperiods were acclimated to low temperatures. Glycerol content in the haemolymph and the crystallization temperature of the muscle and epidermis increased in diapausing larvae reared under short photoperiod, but not in non-diapausing mature larvae reared under long photoperiod. Furthermore, non-diapausing mature and over-wintering (diapausing) larvae were treated with juvenile hormone (JH)-I and 20-hydroxy-ecdysone (20-HE) which regulate larval diapause. When JH-I was applied, glycerol synthesis was activated and the crystallization temperature of the muscle and epidermis rose in non-diapausing mature larvae. However, injection of 20-HE lowered glycerol content and crystallization temperature in overwintering larvae. These results show that glycerol content and ice nucleus production in larvae of the rice stem borer are related to short photoperiod (diapause) and low temperature exposure.

Index terms: Crystallization temperature, freeze-tolerant, diapause

Copyright: The copyrights of this original work belong to the authors (see right-most box in title table). This abstract appeared in Session 13 – INSECT PHISIOLOGY, NEUROSCIENCES, IMMUNITY AND CELL BIOLOGY Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000.