The Study Of The Time Of Invading And Colonizing By Flies In Chongqing And Its Significance In Forensic Application

Objective:To study the time of invading and colonizing by necrophagous flies on mouse carcasses in Chongqing. In addition, to explore its application and significance in death related cases.Methods:Eggs oviposited by blowflies in natural environment were reared for 3 generations. Placed mouse in research field after killing it, at the same time, released two stock colonies of blowflies at the different distance from carcasses and marked in different colors. The effect of different distance from original habitats to carcasses were compared. Different seasons and different time point during a day influenced on invading and colonizing by flies were also observed. This study was replicated in same season.Results:The invasion interval of flies released 100 m away from the carcasses is 152.50 (117.50,555.75) min showed by median M(Q1, Q3), and the colonization interval is 253.00 (186.75,720.50) min. The colony released 1000 m away did not invade the carcasses; The comparison about the invasion interval and colonization interval in different time point showed significant different in some groups. The invasion interval of 9:00 and 14:00 and 21:00 are Tii9 (100.67±61.59 min), Tii14 (133.00±32.39 min), Tii21 (683.83±119.38 min), the colonization interval are Tci (267.50±201.97 min, 198.00±39.41 min,842.83±163.63 min). The comparison between 3 time points (Tii9 vs. Tii14 vs. Tii21, H=11.942, P=0.003; Tci9 vs. Tci14 vs. Tci21, H=11.380, P=0.003) and the comparison between 9:00 with 21:00 (Tii9 vs. Tii21, H=8.308, P=0.004; Tci9 vs. Tci21, H=8.308, P=0.004) and the comparison between 14:00 with 21:00 (Ti14 vs. Tii21, H=8.308, P=0.004; Tii14 vs. Tii21, H=8.308, P=0.004) were significantly different. The invasion interval and colonization interval of 21:00 were delayed compared to 9:00 and 14:00. The invasion interval and the colonization interval of spring and summer and autumn are (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 The comparison about the invasion interval and colonization interval in different season showed no different in comparison of 3 seasons (Tiispr vs. Tiisum vs. Tiiaut, H=0.573, P=0.751;Tcispr vs. Tcisum vs. 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 were affected by different distance from original habitats of flies to carcasses. When the original habitats of flies was too far away from carcasses,flies will not invade carcasses. The change of season did not impact on invasion interval and colonization interval in Chongqing, the main difference was day between 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.