Tolerance To Temperature Stress Of Monochamus Alternatus And Its Potential Suitable Distributions In China

Monochamus alternatus is the main stem boring pest of pine trees in China.It is also the major vector of pine wilt disease(Bursaphelenchus xylophilus),which imposes destructive damages to pine trees.In the process of pine wood nematode’s spread and dissemination,M.alternatus plays a key role in carrying and assisting the invasion to its host.Insect’s growth is restricted and influenced by the environment of invaded habitat.For temperate and frigid zone,the low temperature in winter is the key factor limiting insect’s distribution.According to the information from the State Forestry Bureau in 201 8,the distribution of B.xylophilus in China has gradually expanded,and it has the trend of continuing spreading to north China.Therefore,this paper used insect ecology and physiology method to study different geographic populations of M.alternatus in China and its overwintering larvae in different wintering period.In order to study the cold tolerance difference among different geographic populations of M.alternatus in China and determine low temperature adaptation mechanism and factors,we measured the index of low temperature tolerance,and physiological and biochemical substances.Furthermore,we studied the result of this beetle’s growth which was affected by environment,then we combined it with low temperature exposure experiments.The study divided the potential range with suitable temperature for M.alternatus in China.The following were main results:1.The research identified the differences of index,including supercooling point,freezing point,water content and fat content from six populations of M.alternatus in Yantai,Shandong Province,Fuyang,Zhejiang Province,Zhaoqing,Guangdong Province,Fuzhou,Fujian Province,Yichang,Hubei Province and Dongchuan,Yunnan Province.These indexes were closely connected with cold tolerance.The results showed that the cold tolerance of different geographic populations of M.alternatus was quite different from each other,and also there were significant differences of supercooling point,freezing point,water content,fat content and glycogen content among various groups of M.alternatus.However,the characteristic indexes of cold tolerance like supercooling point and water content have no correlation.2.We could get the conclusion that M.alternatus is non-frozen insect,besides the study showed the dynamic changes of substances related to low temperature tolerance and cold tolerance of M.alternatus larva at different overwintering stages.We found that the over cooling point of M.alternatus larvae during the overwintering period was not obviously changed with the seasonal variation.However,the weight,glycogen content and fat content of the worm showed a trend of decreasing first and rising with the extension of time,and then the water content of the worm increased.3.By low te,mperature exposure experiments,the results presented the semi death time(LLT50)and 99%death time(LLT99)time of larvae under the condition of low temperature exposure with short time(24h)and long time(32d).According to the results,this paper divided highly suitable range,moderate suitable range and unsuitable range of M.alternatus under short-time low temperature stress and long-time lorw temperature stress.We found the cold tolerance difference and physiological and biochemical difference among different geographic populations of M.alternatus in China,determined its physiological and biochemical regulating law during overwintering period.We also provide theoretical guidance for trend prediction of M alternatus in China with division of potential suitable range under low temperature.