Relationship Between Occurrence Of Hessian Fly And Climatic Conditions And Its Heat And Cold Tolerance

Climate factors significantly affect the development of insect population.Climate change will cause the occurrence of pests to increase or decrease.Insect tolerance to extreme temperatures determines their distribution and survival strategies,and affects the occurrence of harm.The Hessian fly,Mayetiola destructor（Say）,is an important quarantine and exotic invasive pest in our country.It was only distributed in local areas of Xinjiang and had repeatedly erupted disaster in history.At present,due to the lack of in-depth research on the relationship between the occurrence of Hessian fly and climatic conditions,and its tolerance to extreme temperature.Understanding the relationship between cold tolerance and heat tolerance of Hessian fly and its occurrence and climate conditions can provide reference for predicting and analyzing its population development and formulating corresponding control strategies.In this study,based on the occurrence data and historical meteorological data of Hessian fly in Wenquan county,Xinjiang,the relationship between occurrence and meteorological factors was analyzed by multiple regression analysis,and the prediction model of occurrence degree and occurrence area rate of Hessian fly was constructed.The heat and cold tolerance of Hessian fly were studied in laboratory.The main research results are as follows:（1）Relationship between occurrence of Hessian fly and climatic factors:Temperature were the main climatic factors affecting the occurrence degree and area rate of Hessian fly.The prediction model of occurrence degree and occurrence area rate of Hessian fly was constructed.The prediction model of occurrence degree was Y₁=0.013-0.106X₁₁₇（R²=0.213）,in which Y₁ was the occurrence degree of current year,X₁₁₇was the average low temperature of late February of that year.The prediction model of occurrence area rate was Y₂=-0.027+0.501X₁₉₈-0.019X₈₁（R²=0.503）,in which Y₂ was the occurrence area rate of the current year,X₁₉₈was the occurrence rate of the previous year,and X₈₁ was the average high temperature in late February of the current year.The historical coincidence rates of prediction models of occurrence degree and occurrence area rate were 44.44%and 66.66%,respectively.（2）Effects of short-term high temperature stress on biology,population sex ratio and eclosion dynamics of Hessian fly:Treatment at 26℃,31℃and 37℃for 3 h/d,5 d had no significant effects on the survival rate,developmental duration,diapause ratio,weight change rate,sex ratio and eclosion dynamics of the 3rd instar larvae.（3）Heat tolerance of larvae:The survival rate of the 3rd instar larvae decreased with increasing temperature and prolonging time after treatment at 40 to 50℃for 1 to 5 h.The Ltem₅₀ at 1 h,2 h,3 h,4 h and 5 h were 44.99℃,43.92℃,42.75℃,42.16℃and 40.92℃,respectively.（4）Cold tolerance of Hessian fly:The SCP at different developmental stages is significantly different,3rd instar larvae<pupa<2nd instar larvae,SCPs were-23.53℃,-22.17℃and-16.78℃,respectively.The SCP of non-diapause larvae（20 d after oviposition）was significantly different from that of diapause larvae（60 d after oviposition,100 d after oviposition,130 d after oviposition）,and decreased with the extension of diapause duration.Cold acclimation significantly decreased SCP of 2nd and 3rd instar larvae,but the effect of cold acclimation on SCP was related to the duration of cold acclimation.There was a significant positive correlation between the weight of the 2nd and 3rd instar larvae and the SCP,while the pupa weight had no significant correlation with the SCP.The protein and sorbitol of the 3rd instar larvae were significantly higher than those of the 2nd instar larvae and pupa.（5）Cold tolerance substance of Hessian fly:The contents of water content,protein,sorbitol and glycogen were significantly different at different developmental stages.The water content of the 3rd instar larvae and pupae was significantly lower than that of the 2nd instar larvae.The protein and sorbitol of the 3rd instar larvae were significantly higher than those of the 2nd instar larvae and pupa.The glycogen content of pupae was significantly lower than that of 2nd and 3rd instars.Combined with SCP results at different development stages,it was speculated that water content,protein,glycogen and sorbitol were the important substances that caused the difference of cold tolerance at different development stages.Cold acclimation of the 2nd instar larvae did not cause significant changes in the contents of fat,glycerol,sorbitol and trehalose.However,with the extension of cold acclimation duration,the water content and glycogen in the 2nd instar larvae decreased significantly,and the protein content first increased and then decreased to the normal level,suggesting that water content,glycogen and protein in the 2nd instar larvae may be involved in the regulation of cold tolerance.With the extension of cold acclimation duration,the contents of water content,glycogen and sorbitol in the 3rd instar larvae significantly decreased,trehalose and glycerol contents significantly increased,protein and fat decreased and increased only after cold acclimation for 1 d.These results indicated that water content,glycogen,trehalose,sorbitol,glycerol were involved in the regulation of cold tolerance of the 3rd instar larvae.The 2nd instar larvae and the 3rd instar larvae have different substances regulating cold tolerance,and the regulation mechanism may be different.In conclusion,the prediction model of occurrence degree and occurrence area rate of Hessian fly was established in this study.It was found that the 3rd instar larvae under short-term high temperature stress had no significant effects on their biological aspects,population sex ratio and eclosion dynamics.It was determined that developmental period,diapause,weight and cold acclimation had significant effects on the SCP of Hessian fly.Seven substances,including water content,which may be involved in the regulation of cold tolerance of 2nd and 3rd instar larvae,were investigated,which laid a foundation for the study of cold tolerance mechanism.These results can provide reference for analyzing the population development of Hessian fly under climate change.