Physiological Profile And Effects Of Temperatue/humidity On Cold-hardiness Of Diapauses Larvae Of Chilo Suppressalis (Walker)

Chilo suppressalis (Walker)(Lepidoptera: Crambidae), is one of the main insect pests in rice.The larvae of Chilo suppressalis enter diapauses in response to short-day cycle. In the currentexperiment, C. suppressalis larvae was induced to diapause under LD12:12on an artificial diet,contents of proteim and nuclear acid in and activities of stress-tolerant enzymes of the diapause larvae,influence of temperature and humidity on cold-tolerance of the diapause larvae and the underlyingphysiological mechnisms, and effects of rapid cold-hardening on cold-tolerance of the diapause larvaewere investigated.The main results are as follows:1. Contents of proteim and nuclear acid in and activities of stress-tolerant enzymes of the diapauselarvaeThe RNA content of diapausing larvae was significantly lower than that of mature larvae, butwas not significantly different among larvae of different diapause duration. DNA content in maturelarvae was significantly higher than those of diapausing larvae. RNA/DNA ratio showed―up-down‖pattern over diapausing time. RNA/DNA ratio in mature larvae was higher than those in diapausinglarvae. Protein content in diapausing larvae was significantly higher than that in mature larvae, but wasnot different among the larvae of diapause duration of1to3months. These results suggest thatdiapausing larva of rice stem borer is characterized by low RNA and DNA contents and high proteincontent. The results also showed that activities of protective enzymes in mature and diapause larvaechanged significantly. Activities of CAT, POD, and SOD were the lowest in mature larvae and thehighest in larvae of2-month diapause duration, while activities of LDH and ATP were the highest inmature larvae and the lowest in larvae of2-month diapause duration.2. Influence of temperature and humidity on cold-tolerance of the diapause larvae and the underlyingphysiological mechnisms(1) Temperature and humidity treatments,5℃at ambient humidity,15℃at30%RH and15℃at90%RH, were set up in climate chambers and diapause larvae at0d were treated at the treatments for20d,40d or60d. It was found that fresh weight and dried weight treated at>5°C for20d weresignificantly lower than those at15°C30%, but the difference between temperatures diminished withprogress of treatment duration. At15℃for20d, fresh weight and dry weight of the diapsue larvaewere higher at the lower moisture condition than at the higher moisture condition, water content was tothe contrary; for the other two treatment duration, differences in weight and water content were notsignificant between treatments.(2) The treatments had significant influence on SCPs and freezing point of the diapause larvae.For all the treatment durations, rank of SCPs and freezing points were5℃<15℃30%RH<15℃90% RH, but significant difference only existed between temperatures.(3) There was no influence of thetreatment on lipid contents of the diapause larvae at various treatment durations.(4) The treatment showed significant influence on glycerol contents. For all the treatmentduration, glycerol content was ranked as:5℃>15℃30%RH>15℃90%RH. The response ofglycogen content to the treatments was to the contrary of glycerol content, which suggests that contentof glycerol is coupled with that of glycogen. The results indicate that low temperature and highhumidity result in decrease in weight and water content of the early stage diapause larvae, but with theprogress of diapause duration, the influence of temperature and humidity is lessened. The results alsosuggest that content of cryprotectant glycerol increase with decrease in temperature and increase inhumidity, content of glycogen shows a different trend, indicating that temperature and humidityinfluence cold-tolerance of the diapause larvae via internal physiological metabolism.3. Effects of rapid cold-hardening on cold-tolerance of the diapause larvaeIt was determined that the discriminating temperature of the diapause larvae reared on anartificial diet was about-14℃, the optimum induction condition for rapid cold-hardening (RCH) was5℃for4h. After RCH, survival rate of diapause larvae at low temperatures were significantly higher thanthose of control groupsThe values of SCPs of the diapsue larvae exposed to the optimum inductioncondition for RCH showed no significant decrease compared to those of the control groups. Survivalrate of the diapause larvae exposed first to the optimum RCH induction condition and then to25℃fordifferent durations decreased significantly when the larvae were tested at the discriminating temperature,which indicates that the duration of the RCH response of the larvae of C. suppressalis was very transientand rapidly diminished after0.5-2h at25℃.