Cold Hardiness And Adaptive Mechanism Of The Anoplophora Glabripennis Larva

The Asian longhorned beetle,Anoplophora glabripennis,is a destructive trunk-borer pest of deciduous broad-leaved species such as Acer(maple),Populus(poplar),Salix(willow),and Ulmus(elm).Larvae mainly bore into tree trunk and overwinter in tree trunk as larvae,seriously affect the plantation,urban forest and farmland protection forest,garden trees growth,cause huge economic losses.Low temperatures in winter have direct effects on overwintering survival,growth,reproduction,and spread of insects,thereby influencing the distribution,number,and population dynamics in the following year.The capacity for cold hardiness is an important prerequisite for the survival,reproduction,and continuation of insect populations.At present,A.glabripennis has gradually spread from the Northwest to the Northeast.However,systematic study about cold hardiness capacity of overwintering A,glabripennis larvae has not been reported previously.This study aimed at revealing the influence factors of cold hardiness,cold type and adaptation mechanism of A.glabripennis larvae.Therefore,the cold hardiness and adaptive mechanisms of A.glabripennis larvae have been researched from the following several aspects in our research.Determination index of cold hardiness ability,physiological and biochemical substances in the body,the expression of heat shock protein gene in larvae from different hosts,different populations,overwintering different periods were researched.The results were as follows:1.The supercooling point(SCP),freezing point(FP),and cold hardiness-related compounds were cleared in overwintering larva from five populations in China(Yili,Yanchi,Wulateqianqi,Beijing,and Dezhou).The supercooling point(SCP)and freezing point(FP)differed significantly among populations,where the SCP of larvae in the Wulateqianqi population was the lowest and highest in the Beijing population.The water,fat,and glycogen contents also differed significantly among the five populations.The SCPs of larvae from all five populations were proportional to glycogen contents,but had no association with water contents and fat contents,The total contents of seven low-molecular weight compounds(glycerol,galactose,glucose,mannose,sorbitol,inositol,and trehalose)differed significantly among populations.Thus.A.glabripennis larvae from different geographical populations contained different sugars or sugar alcohols(especially glycerol,glucose,sorbitol,and trehalose),which helped them to resist cold temperatures.2.Dynamic changes in the supercooling capacity of A.glabripennis larvae in a natural population and the mechanism of cold hardines during different overwintering periods at physiological and biochemical levelswere discribed.The supercooling point of overwintering larvae decreased initially·before increasing subsequently with seasonal changes in ambient temperature.Fresh mass and glycogen tended to decrease initially and then reached their minimum levels in January.Total amounts of low molecular weight substances and free amino acids in the haemolymph increased gradually as the ambient temperature decreased.Glycerol(779.80±29.10μm/mL)and trehalose(104.35±12.38μm/mL)concentrations were always higher than those of glucose and mannitol.All low molecular weight substances(besides trehalose)were almost metabolized by early spring.The concentrations of serine,phenylalanine,valine,leucine,proline,glutamic acid and alanine all reached their highest level in the colder winter months.Anoplophora glabripennis larvae accumulate cryoprotectants to improve their supercooling capacity,and enhance cold hardiness by reducing the supercooling point with respect to a decrease in ambient temperature until freezing temperatures appear.Anoplophora glabripennis larvae are a freeze-tolerant insect.3.Mean SCPs and protein contents of larvae from these three hosts differed significantly.The SCPs and protein contents of the larvae collected from Populus opera and Populus tomentosa were significantly higher than those collected from Salix matsudana.The concentrations of glycerol,glucose and trehalose in overwintering larvae collected from these host species also differed significantly.The larvae that were collected from S.matsudana had the highest concentrations of glycerol and trehalose and those from P.opera the lowest contents of glycerol,126.58±1.18 μg/μL,whereas those from P.tomentosa had the lowest concentrations of trehalose but the highest concentrations of glucose.There were no significant differences in the concentrations of sorbitol and inositol in overwintering larvae collected from these host species.4.The open reading frame(ORF)length of three HSP20s was firstly isolated and cloned from A.glabripennis larvae.It has been clear that the protein sequence of HSP19.77.HSP20.7 and HSP21.64 all have a classic character symbol of HSP20 family,a relatively conservative heat shock structure domain encoding 100 amino acid residues.HSP19.77 and HSP20.7 had high homology with other coleoptera insects,the homology between HSP21.64 and HSP 20 of Phenacoccus solenopsis reach to 80%.HSP 19.77 and HSP 20.7 expressed the highest in coldest month,expression of HSP 21.64 continue to rise until March.This study provides the provide theoretic guidance in clearing life history strategy,physiological biochemical regulation and selection and evolution mechanism,which provide some theory guide on defining the reasons of the emergence and spread,occurrence dynamic and control measures of this population.Meanwhile,this research lay the foundation for further research on molecular regulation mechanism of cold hardiness of A.glabripennis larvae.