Effects of Different Killing Methods on Cricetomys Gambianus in Assessing Insect Fauna Succession and Determination of Postmortem Interval

Abstract

A study was carried out to determine the effects of different killing methods of rat on decomposition, insect succession and determination of postmortem interval. Nine giant rats (Cricetomys gambianus) were used to simulate violent death, natural death and suicide death. One rat was slaughtered to simulate violent death; another was killed by oxygen exclusion to simulate natural death. The third rat was killed by oral injection of 5 ml of 2, 2-dichlorovinyl dimethyl phosphate (DDVP) (common home pesticides) to simulate suicide death. Each of the killing methods was replicated three times and deposited in three sites within University of Nigeria, Nsukka. Decomposition took place under mean temperature and mean relative humidity of 31.05 °C and 71.02 % respectively. The mean decomposition period for violent, natural and suicide death were 30.33±4.67, 48.33±6.67 and 60.00±5.77 days respectively. The arthropod samples collected in this study was 5036 individuals, consisting of 10 orders, 23 families and 50 species. Among the necrophagous families collected were: Calliphoridae, Sarcophagidae, Muscidae, Formicidae, Phoridae, Oestridae, Dermestidae, Cleridae, Curculinidae, Chrysomelidae, Scarabaeidae, Trogoidae, Histeridae, Carabidae, Cucujiformia, Vespidae, Rhipiceridae, Gryllidae, Erebidae, Blattidae, Belostomatidae, Araneae and Rhinocricidae. The arthropods visited the decomposing carcass in the following successional pattern: Formicidae visited after 5 mins of death; Calliphoridae visited after 29 mins; Muscidae visited after 20 mins; Sarcophagidae visited after 2 hrs 45mins; Histeridae visited after 2 days; Dermestidae and other families visited after 4 days and beyond. The greatest number of species was observed in natural death (36 species), followed by suicide death (35 species) and violent death (27 species). The violent and natural death had similar PMI of 9 days after death but in suicide death PMI was 25 days after death. The adult Diptera used in calculating PMI were Chrysomyia albiceps, C. chloropyga and Lucillia sericata in violent death, natural death and suicide death respectively under the fluctuating laboratory temperature and relative humidity range of 23°C - 32°C and 69% - 82% respectively. The PMI of 25 days was caused by overdose of the chemical when compared to the propotion of the size of the animal (rat). The investigation revealed that death due to suicide (chemical intoxication) can delay decomposition and results in PMI error.