Succession pattern of insects in relation to drowning and poisoning of Rattus norvegicus at Delta State University, Abraka, Southern Nigeria

Forensic study using insects is a veritable tool for tracing crime and cruelty cases. In recent times, forensics is gaining local or international attention. Poisoning and drowning are similar criminal cases occurring in Nigeria, thus, this present study determined insects associated with decaying carcasses of rats drowned and poisoned in Site III, of Delta State University, Abraka, Nigeria. Poisoned and drowned rats were positioned at several mapped spots in undeveloped bushy paths close to the uncompleted University library in replicates. Albino Wistar rats of 0.25 to 0.30kg were killed by poisoning and drowning. The carcasses were observed daily, between the hours of 8 am and 6 pm, with a minimum observation time of one hour per sample. A total of 1318 insect belonging to 3 Orders, 6 Families and 7 insect species was encountered in this study. Musca domestica, Sarcophaga albiceps and Calliphora viciniam were common species associated with poisoning and drowning of rats. Six hundred and eighty-nine (689) insects accounting for 52.3% was recovered from drowned rats while poisoned rats accounted for (12.37%) of insect species as compared to control (35.36%). The differences were significant (p < 0.05). More insects were collected during the decay stage of the drowned carcass (53.17%). The overall duration for decomposition was not significantly faster (F= 0.89, p > 0.05) for drowned carcass (mean ± SD= 21.43 ± 9.10 days) in poisoned carcass (mean ± SD= 9.53 ± 1.75 days) and control (mean ± SD= 13.21 ±2.20 days). The results of this present study have shown that poisoning inhibited insect abundance. The occurrence of dipterans in all stages is an indication that they can be adopted as key species to determining poison and drowned carcasses. Though future studies are required studies to confirm this is required to develop the succession status in forensic entomology studies using other animal models.