Research On Cold Resistance And Mechanism Of Holotrichia Parallela Motschulsky

The dark black chafer,Holotrichia parallela Motschulsky,belongs to Coleoptera:Melolonthidae.The larvae,commonly called white grubs,are important underground pests of a wide range of crops and trees,including food crops,cash crops,oil crops,vegetables and fruit trees.Except Tibet,the grubs distributed nearly all over the China.In recent years,along with the expansion of conservation tillage in large areas,which includes shallow loughingp,no-tillage and plastic mulching,Holotrichia parallela has become one of the dominant species of underground pests,and causing more and more serious damage.Researched cold resistance and physiological ecological mechanism about Holotrichia parallela in this Research.It provided a theoretical basis to understand the mechanism for belowground vertical migration behavior of H.parallela in winter,explained the ecological characteristics of the strong adaptability and wide distribution.The main results are as follows:(1)The supercooling point(SCP)and freezing point(FP)of H.parallela in different overwintering stages were determined.Among them,the supercooling point of the mature larvae and adult was-7.23 ? and-7.68 ?,respectively.The freezing point of body fluid was-5.70 ?and-5.93?,respectively.There was no significant difference(P>0.05)between mature larvae and adults in SCP and FP.However,comparing to the cold-resistant insects,the dark black chafer's cold resistance is relatively low,which means it cannot overwinter in the north of China outdoor winter environment.(2)The mature larvae were pretreated at 4 ? for 30 days to determine the SCP and FP.Results showed that the low temperature pretreatment had no significant effect on the supercooling point and the freezing point of the larvae(P> 0.05).It belongs to the freezing-susceptibility insects were conformed.When compared with H.oblita,the supercooling and freezing points of the mature larvae in H.parallela were significantly lower than that in H.oblita(P<0.05).It suggests that mature larvae of H.parallela were more resistant to low temperature than H.oblita.However,there was no significant difference on the SCP and FP between adult of the two species,which means the cold resistance was similar.(3)It revealed that low temperature has a significant effect on the survival rate of the mature larvae.Mortality of the tested larvae increased significantly with the extension of the treatment time at 12?,8?,4?,0? and-4?.With the decrease in treatment temperature,the mortality at the same treatment time showed a gradual increase.The mortality was more than 50% under the condition 0? for 72.h,and was 100% at-4? for 72 h.It indicated that,the critical temperaturefor H.parallela mature larvae surviving was above 0?.(4)The changes of biochemical substances in the mature larvae of H.parallela studied under different low temperature treatments.The content of fat decreased at 12?,8?,4? and 0? for72.h,but there was no significant difference between different low temperature treatments and the control(P > 0.05).The contents of free water and total protein in larvae were not significantly changed after 72.h treatment at different low temperatures(P > 0.05).With the decrease of the treatment temperature,the content of the cold resistance small-molecule compounds,such as Trehalose and 3-?-Mannose,increased at the beginning and then decreased with the dropping of treatment temperature.While Myo-inositol decreased at the beginning and then increased with the dropping of treatment temperature.In addition,there was no significant difference between different treatments and the control(P>0.05).(5)Analyzed the effects of different low temperature treatments on the activities of related enzymes changes in H.parallela mature larvae.The mature larvae were treated at 12?,8?,4?and 0? for different times.With the decrease of treatment temperature,the activity of superoxide dismutase(SOD)in the larvae of the mature larvae showed the trend of decreasing first and thenincreasing;the activity of peroxidase(POD)and catalase(CAT)showed a rising trend.However,no significant differences were founded in activity of the three kinds of enzymeswere not found between different low temperature treatments groups and the control(P>0.05).(6)In conclusion,determined the strategy of H.parallela adapting to the winter low temperature circumstance(ecological adaptation strategy)belongs to behavioral strategy.