重庆地区尸食性蝇类侵袭建群时间初步研究及法医学意义

Time of invading and colonizing of necrophagous flies in Chongqing and its significance in forensic application

目的:研究重庆主城区嗜尸性蝇类侵袭动物尸体并在其上建立群落的时间规律,探索其在死亡相关案件中的应用价值与意义。方法:在野外引诱丽蝇产卵,连续培养3代,建立封闭群。处死大鼠后放置野外,在距尸体不同距离地点同时释放2个封闭群,并分别标记。比较不同距离的蝇类原始栖息地、不同季节、不同时刻死亡的动物尸体对蝇类侵袭及建群时间的影响,每组实验重复1次。结果:距离大鼠尸体100 m处释放的蝇类侵袭尸体的时间用M(Q_1,Q_3)表示是152.50(117.50,555.75)min,在尸体上建群的时间用M(Q1,Q3)表示是253.00(186.75,720.50)min,距离大鼠尸体1 000 m处释放的蝇类未对大鼠进行侵袭及建群。在比较不同时刻处死大鼠和不同季节处死大鼠对蝇类侵袭尸体及建群影响时:9时、14时及21时3组的侵袭时间分别是T_(ii9)(100.67±61.59)min、T_(ii1)4(133.00±32.39)min、Tii21(683.83±119.38)min,建群时间分别是Tci(267.50±201.97)min、(198.00±39.41)min、(842.83±163.63)min。不同时刻的蝇类侵袭及建群时间的3组间比较(T_(ii9)vs.T_(ii14) vs.Tii21,H=11.942,P=0.003;Tci9vs.Tci14vs.Tci21,H=11.380,P=0.003)均存在差异,9时与21时的侵袭及建群时间比较(T_(ii9)vs.T_(ii21),H=8.308,P=0.004,T_(ci9) vs.T_(ci21),H=8.308,P=0.004)均存在差异,14时与21时的侵袭及建群时间比较(T_(ii14)vs.T_(ii21),H=8.308,P=0.004,T_(ii14)vs.Tii21,H=8.308,P=0.004)均存在差异,21时蝇类对尸体的侵袭及建群时间长于9时与14时的时间。春、夏、秋3组侵袭时间及建群时间分别是(293.83±314.74、289.00±206.30、334.67±365.76,339.83±331.48、489.17±214.07、479.33±444.22)min。不同季节对蝇类侵袭及建群的3组间比较不存在统计学差异(T_(ii春)vs.T_(ii夏)vs.T_(ii秋),H=0.573,P=0.751;T_(ci春)vs.T_(ci夏)vs.T_(ci秋),H=1.556,P=0.459),季节对蝇类的侵袭及建群时间无明显影响。结论:位于尸体不同距离的蝇类对尸体的侵袭及建群时间有影响,较远的距离会延迟蝇类对尸体的侵袭及建群,甚至不发生侵袭;重庆地区季节的变化对蝇类侵袭尸体及建群时间没有明显的影响,主要是白天和黑夜的差异,黑夜会延长蝇类侵袭尸体及建群的时间。本研究结果对命案现场中根据尸体的具体情况准确推断死亡时间有指导意义。

Objective：To study the time of invading and colonizing of necrophagous flies on mouse carcasses in Chongqing and to explore its application and significance in death related cases. Methods：Eggs oviposited by blowflies in natural environment were reared for 3 generations. Mice were killed and placed in research field. At the same time,two stock colonies of blowflies were released at the different distances from carcasses and marked in different colors. The effects of different distances from original habitats to carcasses were compared. Effects of different seasons and different time points on invading and colonizing of flies were also observed. This study was replicated in same season. Results：The invasion interval of flies released 100 m away from the carcasses was 152.50（117.50,555.75）min showed by median M（Q_1,Q_3）,and the colonization interval was 253.00（186.75,720.50）min. The colony released 1 000 m away did not invade the carcasses. The comparison about the invasion interval and colonization interval in different time points showed significant differences among some groups. The invasion intervals of 9：00,14：00,21：00 were T_（ii9）（100.67±61.59）min,T_（ii1）4（133.00±32.39）min,T_（ii21）（683.83±119.38）min;the colonization intervals of 9：00,14：00,21：00 were T_（ci9）（267.50±201.97）min,T_（ci14）（198.00±39.41）min,T_（ci21）（842.83±163.63）min. The comparison between 3 time points（T_（ii9） vs. T_（ii14） vs. T_（ii21）,H=11.942,P=0.003;T_（ci9） vs. T_（ci14） vs. T_（ci21）,H=11.380,P=0.003）and the comparison between 9：00 with 21：00（T_（ii9） vs. T_（ii21）,H=8.308,P=0.004,Tci9 vs. Tci21,H=8.308,P=0.004）and the comparison between 14：00with 21：00（T_（ii14） vs. T_（ii21）,H=8.308,P=0.004,T_（ii14） vs. T_（ii21）,H=8.308,P=0.004）were significantly different. The invasion interval and colonization intervals of 21：00 were delayed compared with those of 9：00 and 14：00. The invasion interval and the colonization intervals of spring and summer and autumn were（293.83±314.74）min,（289.00±206.30）min,（334.67±365.76）min;（339.83±331.48）min,（489.17±214.07）min,（479.33±444.22）min. The comparison about the invasion interval and colonization intervals in different seasons showed no difference in comparison of 3 seasons（Tiisprvs. Tiisumvs. Tiiaut,H=0.573,P=0.751;Tcisprvs. Tcisumvs. Tciaut,H=1.556,P=0.459）. The seasons did not impact on invasion interval and colonization interval. Conclusion：The invasion interval and colonization interval are affected by different distances from original habitats of flies to carcasses. Flies will not invade carcasses when the original habitats of flies are too far away from carcasses. The change of season will not impact on invasion interval and colonization interval in Chongqing;the main different is day and night;the night could delay invasion interval and colonization interval. This research is important for determining postmortem interval accurately according to actual circumstance in the crime scene.