Study On Physiology Responses And Fitness Of Offsprings To Rapid Cold Hardening Of Harmonia Axyridis (Coleoptera: Coccinellidae)

Harmonia axyridis Pallas(Coleoptera:Coccinellidae),due to its strong ability in ecological adaptability and hunting a large number of pests,it's regarded as promising predatory insect in integrated pest managment.The promition of in artifical mass rearing of H.axyridis has played a significant role in promoting the deveiopment of ecological agriculture.Global warming increases the probability of sudden change of temperature in local areas,under natural conditions,H.axyridis is more sensitive to low temperatures under natural conditions and is more affected by short-term temperature fluctuations.In this paper,we focus on the physiological response of rapid cold hardening(RCH)and the fitness of offsprings for the H.axyridis,successfully selected the optimal acclimation dose for short-time constant temperature and gradient cooling,then preliminary determined the relevant physiology and biochemistry variations in male and female adult of H.axyridis after RCH,and figure out the influence on the fitness of offsprings.It could provide theoretical informations for study the cold tolerance of H.axyridis and the cold acclimation of natural enemy insects.The major results of this thesis are summarized as following:1.Selection and sustained determination of optimum dose of RCH for H.axyridis adultAfter different short-term cold acclimation for H.axyridis,increased their survival rate at the recognition temperature of-10°C/2 h,the optimal constant temperature does was 0°C/4 h,and the survival rate was increased from 33.13%(without cold acclimation at-10°C/2 h)to 77.50%;for equal gradient cooling treatment at 10°C-5°C-3°C-0°C the best dose was 2 h,and the survival rate was increased to 75.63%.There was no significant difference in the survival rate of gradient cooling treatment 8h compared with0°C/2 h,indicating that gradient cooling of H.axyridis adult did not further increase their survival rate on a constant temperature basis,and there was no increase in efficiency in the overlapped temperature section.The cold acclimation effect was also disapperd after RCH of H.axyridis,under the optimal dose treatment,the cold effect at 0°C/4 h last for 7days,the gradient cooling effect was about 5 days at 2 h.2.Physiological response to RCH of H.axyridis adultBoth cold acclimation methods can reduce the SCP and water content of adult of H.axyridis,but only the 0°C/4 h treatment group reaches a significant level in males,and the others have no significant changes.The body fat content of insects has a downward trend,but it is not significant,which indicates that RCH is not enough to make the adult of H.axyridis consume large amounts of fat to protect the cold.RCH can accumulate small-molecule carbohydrates for H.axyridis,such as glucosamine,trehalose,glycerol,and mannitol increase significantly both male and female adults,and largest increase in males.However,fructose content was only significantly increased in the gradient cooling treatment group,indicating that fructose is a kind of antifreeze protection material under the rapid gradient cooling of H.axyridis.Sorbitol decreased slightly in both modes and did not show significant changes.The glycogen content decreased significantly,showing that glycogen is the main energy-consuming substance in the process of RCH for H.axyridis.Therefore,the adult of H.axyridis experenced short-time cold acclimation and formed the cold-resistant system of glycogen-glucose-trehalose-mannitol-glycerol.Both short-term cold acclimation methods affected the activities of antioxidant enzymes and glycolytic enzymes in the adult of H.axyridis,the activities of superoxide dismutase(SOD)and catalase(CAT)were significantly enhanced,while the peroxidase(POD)activity was opposite to the trend of the two.There was a significant difference in male SOD between the two cold acclimation methods,and the activities of other enzyme had no difference,it showing that the change of short-term cold acclimation the activity of antioxidant enzymes are not correlate with the acclimation methods.The glycolysis-associated lactate dehydrogenase(LDH)activity is severely reduced under both treatments and is more pronounced in males,indicating that the insect is slowing down its own metabolism.The Na~+K~+-ATPase activity associated with transmembrane transport is basically stable near the fixed domain value,but there is a rising trend.In summary,it can be seen that RCH has a significant effect on male adults of H.axyridis compared to females;the effect of different acclimate processes of RCH on H.axyridis didn't reach significant levels.3.Effect of RCH on the fitness of H.axyridis offspringsThe effects of RCH could extend across generations,compared with the control,the developmental duration of the eggs and the third instar larvae of F1 that from acclimated parents were prolonged and the 0°C/4 h acclimation group had significantly shorter for the developmental duration in fourth-instar larvae and pupa.But there was no difference between the pupation rate,emergence rate,pupa weight,adult weight.RCH has a greater effect on sex ratio of offsprings,and the proportion of females after emergence was higher than that of the control.The fertility rate of females in the cold acclimation group was reduced,however,the Preoviposition and the first fecundity was no difference,30days cumulative fecundity was only slightly lower at the 0°C/4 h acclimation group,but the difference is not significant.The two short-term cold acclimation had no negative impact on the predation behavior of F1 generation fourth instar larvae and adults,nor do they increasing the daily predation amount compensate for the nutrient loss that was caused by cold acclimation on the parental generation.