Tolerance And Adaptability Of Larval Rice Leaf Folders To Heat Shock

Temperature is an important factor that affects the occurrence and development of rice leaf folder(RLF)Cnaphalocrocis medinalis population.Under the trend of global warming,effects of high temperature on the RLF populations will become stronger.There have been some researches on effects of heat shock on RLF's egg,pupae and adult stages,but the tolerance and adaptation of RLF larvae to heat shock are still unclear.Therefore,the range of high temperature and duration of exposure which RLF larvae could tolerate,the post-effects of heat shock on larvae,and the ability of heat acclimation of RLF were examined in this study,using the population reared in laboratory.The results have been listed as following:(1)The results showed that heat shock had a lethal effect on RLF larvae,but larvae overall were relatively heat-resistant.When the first instar larvae were exposed to 39?,lethal exposure time 50%(LET50)to heat shock was 12.6 h,and when the heat shock kept 2 and 3 days,the LET50 were 8.12 h per day and 6.22 h per day,respectively.When the first instar larvae were exposed to 41?,the LET50 was 4.32 h in one day,or 2.81 h per day lasted 2 days.The tolerance of RLF larvae in different instars was different to high temperature.The tolerance of old larvae was higher than that of young ones.Under the same conditions of heat shock,the survival rates of the 2-3 and 4-5 instar larvae were significantly higher than that of the first instar larvae.When the 2-3 instar larvae were exposed to 39? for three days with 11 h per day,the survival rate was still more than 50%,and the mortality rate of 4-5 instar larvae was less than 50%until they were exposed to 39? for three days with more than 7 h per day.RLF larvae have strong heat resistance.In summer,the high temperature in Jiangsu province would be not strong to result in a lethal effect on RLF larvae.(2)The post-effects of heat shock on young larvae were very less.Heat shock at 39?for three days with 8 h per day,or at 41? for 9 h,or 41? for two days with 3 h per day to the first instar larvae,the survival rates,pupation rates,emergence rates,adult longevity,fecundity and hatchability for these larvae which survived after heat shock were not significantly different among heat shock and control.The survival rate,pupation rate,emergence rate and fecundity were not affected by the heat shock in the first instar larvae by 41? for two days with 5 h per day,although the heat shock significantly prolonged the adult's longevity and reduced hatchability.The negative post-effects of 39 and 41? high temperatures for the first instar larvae of RLFs were not found in this study.When the 2-3 instar larvae of RLF were exposed to 39? for 3-11 h,their pupation rates,eclosion rates,adult longevity,fecundity and hatchability were not affected by the heat.When the high temperature of 39? lasted for two days with 3-9 h per day to the 2-3 instar larvae,the pupation rate,fecundity and hatchability were not affected,but it reduced the eclosion rate and adult longevity.When the 4-5 instar larvae of RLF were exposed to 39? for 3-7 h,those survived larvae did not appear a significant effect in their biological traits,but the heat shock lasted for 9-11 h significantly reduced the hatchability of their eggs.The high temperature of 39?for two days with more than 7 h per day significantly reduce the pupation rate,eclosion rate and hatchability,but no effects on fecundity were found.The high temperature of 39? for three days with 5 h per day or more,the pupation rate,eclosion rate and fecundity were significantly reduced.The obvious negative post-effects of heat shock for old larvae of RLF were found.High temperature of 41? suppressed the feeding behaviour of the 3 and 4 instar larvae of RLF.The feeding amount of 3 and 4 instar larvae in the exposure to 41? for three days with 3 h per day was significantly less than the control at 27?.The feeding ability could not be fully restored after three days of heat shock,and the feeding amount was significantly lower than that of control.(3)The survival rates of the first instar larvae of RLF increased when they were exposed to 39? for three days with 3 h per day and this heat shock maintained five generations,and the survival increased from 0.42 in the first generation to 0.74 in the fifth generation.First instar larvae exposed to 41?(3 h per day)for three days in continuous five generations,their survival rates increased during 1-4 generations,but declined during the fifth generation.Heat shock acclimation under 39? for the first instar larvae by five generations did not affect the adult longevity,fecundity and hatchability,but under 41?,the fecundity and hatchability decreased.