Study On The Changes Of Sarcosarprophagous Insects And Carcasses In The Yangtze River Delta Region

Time since death also known as postmortem interval?PMI?,is extremely relevant to criminal activities,and in most cases,it is identical to the time of crime.Therefore,the PMI is extremely significant in identifying or eliminate a suspect,and to mark out an investigative area.But for a long time,the PMI,especially the PMI during the stage of advanced-decay or remain,is an unsolved problem in forensic medicine.The forensic entomology provided a way to solve the problem of PMI,and the relevance theories,including the patterns of insect succession and development,are widely used in determining the PMI.Therefore,investigating insect succession,along with developmental study of carrion insects,constitutes some of the most fundamental and important work of forensic entomology.In this thesis,the insect succession and development of forensciall important insects of Yangtze River Delta were studied.The results are summarized as follows:1.Body decomposition and insect succession of carcasses exposed at different time of a dayEighteen pigs carcasses?about 15 kg?were exposed at 6 time points during the day:10:00,14:00,18:00,22:00,02:00 and 06:00 on September 8th-September 9th in a field near the Forensic Autopsy Center of Suzhou,China?31°21'N,120°53'E?to investigate the potential effect of the time of day of carcass exposure on the colonization of Calliphoridae,body decomposition and insect fauna.The results show that the flies have strong circadian rhythms.The nocturnal activity and oviposition was not observed during the study.Due to the gap of the night,the larval Chrysomya megacephala?Fabricius?were divided into several batches with different developmental process.We found three batches of C.megacephala on carcasses a and b,while we only found two batches of C.megacephala on carcasses c,d,e and f.The three batches of larvae on carcasses a and b formed a much stronger competition,leading to a large number of larvae crawl away from the carcasses.So in the late stage of decomposition,the carcasses a and b remains unexpected more soft tissues than the carcasses c,d,e and f.The remaining tissues provided favorable conditions for the colonization of later arrival Diptera and Coleoptera,so the taxa number of larval Diptera and Coleoptera on carcasses a and b were more abundant than those on carcasses c,d,e and f.The results indicate that there is a very close link between the carcasses and the insects,and one of the minor changes will affect the whole process of body decomposition and insect succession.This study not only explained the effect of the time carcasses exposed on body decomposition and insect succession,but also provided basic data of insect succession for the autumn of Yangtze River Delta.2.The development of three forensically important speciesDuring the field study,the forensically important insects,including Lucilia illustris Meigen,Creophilus maxillosus L.and Boettcherisca peregrina Robineau-Desvoidy,were collected,and the laboratory colonies were established.These insects were reared under different constant temperature to investigate the indexes of development duration,larval body length and accumulated degree hours.Using these results,we generated three development models,including isomorphen diagram,isomegalen diagram and thermal summation model.The threshold temperature?D₀?and thermal summation constant K was determined using the thermal summation model.Through regression analysis,simulation equations of the variation in larval body length with time after oviposition?larviposition?,and variation in time after oviposition?larviposition?with body length were obtained.The results of these studies provided some basic data for the use of development patterns of insects for estimating PMImin.3.Intra-puparial development and differential gene expression during the pupal stage of L.illustrisThe pupal stage of L.illustris which represents about 50%of the immature developmental phase was aging using two methods,including morphological observation and quantitative real time PCR.The intra-puparial morphological changes of entirety pupa of L.illustris was divided into 12 sub-stages,and the intra-puparial morphological changes of compound eyes,mouthparts,antenna,thorax,legs,wings and abdomen was divided into6-8 stages using morphology method.The different stages correlated with time were observed and recorded.The expression level of three target gene?actin,15₂ and tbp?during the pupal stage of L.illustris was studies.The results show that the expression of the three target gene was in a regular pattern,and can be used as an indicator for age estimation of the pupal stage,while the expression level of these target genes can determine a more accurate pupal age when combined with the intra-puparial morphological changes.These results provide an important basis for the use of pupal development-based estimation of the minimum postmortem interval?PMImin?in forensic entomology.