| Objective:After the death of human and other animals,the sarcosaprophagous insects are attracted to the corpses,then colonize the corpse and finish their development.Therefore,the development and succession patterns of sarcosaprophagous insects can provide a basis for estimating the minimum postmortem interval(PMImin).Necrobia ruficollis(Fabricius)(Coleoptera:Cleridae),Hermetia illucens(L.)(Diptera:Stratiomyidae)and Piophila megastigmata(McAlpine)(Diptera:Piophilidae)are forensically important insects,which mainly active in the middle and late stage of decomposition,or even at the skelentonization stage.As a result,research on these insects can improve the accuracy of PMI estimation in the middle and late stage of decomposition and provide a scientific basis for PMI estimations for highly decomposed and skeletonized corpses.This study aims to obtain development data by studying the development of three species under different constant temperature,and further establish the related time of death inference model,in order to provide a basis for the PMI estimation in actual cases.Method:1.The N.ruficollis adults of this study were collected from pig carcasses in the field succession experiment and brought back to the laboratory to establish a laboratory population.They were raised in five different constant temperature conditions to observe and record their development duration.In vivo measurement was used to measure the changes of larval body length with development time under different constant temperature conditions.We also monitored the widths of the head capsules and the distance between the urogomphi of larvae to infer the larval instars.Linear and nonlinear models were used to construct the accumulated temperature models for its growth and development,and the developmental threshold temperature and accumulated temperature constants of each developmental stage were calculated.The Isomorphen model of the development time of N.ruficollis was further established based on the data.According to multiple regression analysis,the calculation formula of the time required for larval development to a specific body length was fitted,and the Isomegalen model of the length of larval precursors from hatching to pupal chamber was constructed.The relationship between different instars of larva and the widths of head capsule,the distance between the urogomphi was determined by cluster analysis,which could be used to infer larval instars.2.The laboratory population of H.illucens was raised from eggs purchased from the breeding site after several generations of breeding.They were raised in six different constant temperature conditions to observe and record their development duration.We monitored the changes of the body length of the larvae with the development time.Linear and nonlinear models were used to construct the accumulated temperature models for its growth and development,and we calculated developmental threshold temperature and accumulated temperature constants.The Isomorphen model of the development time of H.illucens was further established based on the data.According to multiple regression analysis,the calculation formula of the time required for larval development to a specific body length was fitted,and the Isomegalen model of the length of larval precursors from hatching to pupal chamber was constructed.3.The P.megastigmata adults of this study were collected from pig carcasses in the field succession experiment and brought back to the laboratory to establish a laboratory population.They were raised in six different constant temperature conditions to observe and record their development duration.We monitored the changes of the body length of the larvae with the development time under different temperature.Linear and nonlinear models were used to construct the accumulated temperature models for its growth and development,and we calculated developmental threshold temperature and accumulated temperature constant.The Isomorphen model of the development time of P.megastigmata was further established based on the data.According to multiple regression analysis,the calculation formula of the time required for larval development to a specific body length was fitted,and the Isomegalen model of the length of larval precursors from hatching to pupal chamber was constructed.Result:1.N.ruficollis can finish development under the constant temperature of 22-34℃.In the temperature range of 22-31℃,the development rate was gradually accelerated with the increase of temperature,but when the temperature rose to 34℃,the development of N.ruficollis was delayed,and the development rate was slower than that of 31℃.Based on the growth and development data,linear and nonlinear accumulated temperature models,Isomegalen model and Isomorphen model were established,which can be used to estimate PMImin.Based on the linear accumulated temperature model,we obtained accumulated temperature constant and developmental threshold temperature of each developmental stage and the whole stage from egg to eclosion.The upper developmental temperature TH,lower developmental temperature TL and internal optimal temperature Tφ were obtained by nonlinear model.The widths of the head capsules and the distance between the urogomphi of larvae at different instars can be determined by cluster analysis.2.H.illucens can finish development under the constant temperature of 19-34℃.In the temperature range of 22-31℃,the development rate was gradually accelerated with the increase of temperature,but when the temperature rose to 34℃,the development of H.illucens was delayed,and the development rate was slower than that of 31℃.Based on the growth and development data,linear and nonlinear accumulated temperature models,Isomegalen model and Isomorphen model were established,which can be used to estimate PMImin.Based on the linear accumulated temperature model,we obtained accumulated temperature constant and developmental threshold temperature of each developmental stage and the whole stage from egg to eclosion.The upper developmental temperature TH,lower developmental temperature TL and internal optimal temperature Tφ were obtained by nonlinear model.In this paper,the development data of Black horsefly at home and abroad under different rearing conditions were compared.3.P.megastigmata can finish development under the constant temperature of 19-34℃.In the temperature range of 22-28℃,the development rate was gradually accelerated with the increase of temperature.However,there was no significant difference in development rate between 28℃ and 31℃.Also,the growth rate at 34℃ is slower than that at 31℃.Based on the growth and development data,linear and nonlinear accumulated temperature models,Isomegalen model and Isomorphen model were established to estimate PMImin.We obtained developmental threshold temperature and accumulated temperature constant of each developmental stage and the whole stage from egg to eclosion,which based on the linear accumulated temperature model.The upper developmental temperature TH,lower developmental temperature TL and internal optimal temperature Tφ were obtained by nonlinear model.Conclusion:1.It is the first time in China to study the development of N.ruficollis.The body length,the widths of the head capsules and the distance between the urogomphi of larvae were measured by in vivo method.Based on the data,the Isomorphen model,accumulated temperature model and Isomegalen model of body length change,and the classification model for larval instar were established.2.This study provided the development data of H.illucens under the condition of "raw meat+oat" diet,and established the Isomorphen model,accumulated temperature modeland Isomegalen model for predicting the time of death.It is the first time to provide a curve model and formula to infer larval age from larval body length.3.This study provided the development data of P.megastigmata.For estimating PMImin,we established the Isomorphen model,accumulated temperature model,Isomegalen model and its inferred formula. |
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