Study On The Development Of Chrysomya Rufifacies And Necrobia Rufipes In Estimating Postmortem Interval

Objective:After the death of humans or animals,the odors released at different stages of decay attract various insects,and other arthropods,to the corpses.Therefore,the development of insects,and other arthropods present on corpses,can be assessed to estimate the minimum postmortem interval(PMImin).Chrysomya rufifacies(Macquart)(Diptera:Calliphoridae)and Necrobia rufipes(De Geer,1775)(Coleoptera:Cleridae)are forensically important insects that have been found on almost all remains.The objective of this study is to obtain development data and establish developmental model to estimate PMImin by studying the development of C.rufifacies and N.rufipes under different constant temperature,so as to provide important application data for PMImin estimation in practical cases.This study also reports a case using the developmental data of insects collected from a corpse concealed in a suitcase and combining succession pattern to estimate the PMI,and to provide a reference to similar cases.Method:(1)In this study,C.rufifacies larvae were cultured under different constant temperaturecondition in the laboratory to observe and record the development history,and to measure the changes of the body length of larvae with the development time in different constant temperature.Equations for PMImin estimation were simulated using non-linear regression analysis.Based on the equation,the time required for the body length of larvae to grow to the same length under different constant temperature was calculated,and the isomegalen model from hatching to the wandering was established based on the data.The isomorphen model was based on data on the time it took for the C.rufifacies to develop to different developmental landmark under different constant temperature condition.According to the developmental duration of different developmental stages,including egg,first instar larva,second instar larva,third instar larva and pupa stage,the thermal summation model was established using linear regression analysis,and the thermal summation constant and the developmental threshold temperature of different developmental stages were calculated.In addition,the data and model obtained from this study were applied to the actual cases for estimating PMImin.(2)In this study,a laboratory population was established by collecting N.rufipes adults from field succession experiment on pig carcasses.N.rufipes were cultured in different constant temperature condition in lab.Larvae were individually fed and developmental duration were monitored and recorded.The change of the larval body length,as well as the widths of head capsule,pronotum,and mesonotum with development time under different constant temperature environment were monitored.The isomorphen model was established based on the data of the time it took for the development of N.rufipes to different developmental landmark under different constant temperature condition.The equations and growth curves of the relationship between the larval body length and the widths of mesonotum,and the development time were simulated using nonlinear regression analysis.The isomegalen model of larva from hatching to pupal chamber formation was established based on the time required for the larva to develop to an identical length and width in different constant temperature condition.According to the developmental duration data of different developmental stages,the thermal summation model was simulated by linear regression analysis,the thermal summation constant and the developmental threshold temperature of different developmental stages were calculated according to the thermal summation model.Through cluster analysis,the widths of head capsule,pronotum of different instar larvae were determined,so as to facilitate the prediction of the instar of larvae.The discriminant classifier was established by linear discriminant analysis and its discriminant accuracy is verified.(3)In this study,the insect samples collected from the crime scene were taken to the laboratory for analysis,and the corresponding development and succession data in combination with the field temperature and other environmental factors to estimate PMI.Result:(1)C.rufifacies can develop at a constant temperature between 16-34℃.At 16,19,22,25,28,31 and 34℃,the development rate is accelerated as the temperature increases.Based on the experimental data,isomorphen model,isomegalen model and thermal summation model were established.According to the thermal summation model,the developmental threshold temperature and the thermal summation constant of six developmental stages and the total developmental process from egg to adult were obtained.The time of death of the victim in a criminal case was accurately inferred by using the data of this study.(2)Under a constant temperature condition of 22-36℃,the development rate of N.rufipes increased with increasing temperature,but there was no significant difference between the development time at 31℃ and 34℃.Using experimental data,isomegalen models,isomorphen models,and thermal summation model at various stages of development were established for estimating PMImin using N.rufipes.The widths of head capsules and pronotum of larvae at different instars were determined by cluster analysis.Classifiers were created and validated by linear discriminant analysis(LDA).(3)We estimated the PMI based on the insect development and succession data,combined with field temperature and other environmental factors,and the results consistent with the actual time of deathConclusion:This study provides detailed developmental data on the population of C.rufifacies in the Yangtze river delta region of China,and isomegalen model,isomorphen model and thermal summation model at each developmental stage were established for estimating PMImin.In this study,the development of N.rufipes was studied in the laboratory under different constant temperatures.In vivo measurements were conducted to monitor the morphological changes of N.rufipes.larvae during development.Isomegalen model,Isomorphen model,and thermal summation model were established.The predictive classification of the observed samples was conducted according to this discrimination function.The total accuracy of the discrimination function was good.When estimating PMI based on insect evident,it is necessary to consider insect development data and insect succession pattern,as well as temperature and other environmental factors,and biology habit.