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Background & Objective:Postmortem interval has been a problem in the work of forensic autopsy, and it is an important issue of Forensic research. Forensic entomology has rapidly developed in every country since the 1980s. So many researches indicated that the methods of estimation of postmortem interval based on the necrophagous flies are relatively efficient and accurate. On the bases of the former researches, the purpose of this research is by observing the development of the three most common species(Lucilia sericata, Chrysomya megacephala, Boettcherisca peregrine) of necrophagous flies in Zhengzhou, in order to find out the relationship between the length of larvae and growth time, which can be used for the estimation of the postmortem interval in Zhengzhou City.Methods:1. Put the fresh liver tissue in a glass container once three days;2. Observed the situation of the necrophagous flies every tow hours. Recorded the species of the necrophagous flies that spawned on the culture medium and the time of the first spawned;3. Observed and measured the length of the maggots after spawned of the necrophagous flies every 12 hours until the maggots become pupas, and recorded the temperature and humidity;4. Finally, observed and recorded the time of the pupas hatched into flies;5. Analysis the data used Statistical software (spss10.0).6. Observe the activities and the spawning behavior of the necrophagous flies in different environments (day, night, indoor, outdoor, rain, winter, tightly wrapped, etc.), and study the factors that affect the spawning behavior of necrophagous flies.Results:1. In this experimental time, there were three species of necrophagous flies appeared and spawned on the culture medium in Zhengzhou. The activity and spawning behavior of their are different in every season:Lucilia sericata is from April to November, Boettcherisca peregrine is from May to October, Chrysomya megacephala is from March to November. Although some necrophagous flies can reach the culture in winter (December to February), but they can’t lay eggs because of the low temperature. Instead at higher temperatures the type and number of the necrophagous flies are complicated.2. The times of one growth cycle of these necrophagous flies are very different because the temperatures of each month were very difference. In addition, this study also found that the growth rate of maggots can be affected if the temperature sudden drop in one growth cycle, their growth rate slowed down with the decrease of temperature, otherwise the growth rate is increase for the high temperature. We analyzed these experimental data by statistical software, draw the correlation coefficient and regression equation of the fly larvae’s length and growth time in larva stage; and find out the growing curves of maggots of necrophagous flies in every months.3. By observing the spawning behavior of the necrophagous flies in different environments, we found there is spawning of necrophagous flies during the environments of the day, cloudy and after rain. During night or light rain, although the necrophagous flies can act but they didn’t lay eggs. In heavy rain and moonless night the necrophagous flies aren’t appeared. With the increases of altitude the quantity of spawned become fewer. The spawning of necrophagous flies indoors was later than outdoors. In winter, we neither find the necrophagous flies activity, nor find their lay eggs.Conclusion:1. There have some seasonal differences among different species of necrophagous flies (Lucilia sericata, Boettcherisca peregrine, Chrysomya megacephala). The growing development laws of the larvae are different, and the growing development rate was shortened with the temperature increased.2. The spawning behavior of necrophagous flies were influenced by some environmental conditions. In short, during the time of estimating the postmortem interval using the growing development law of necrophagous flies, we should fully understand the change of environment around the corpse.
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