Etude de l’arthropodofaune nécrophage des cadavres emballés de porcs domestiques à Malombo dans la Région du Centre- Cameroun: applicabilité dans la datation des dépouilles

Abstract

When an animal dies, it is quickly visited and colonized by many organisms such as bacteria, fungi, arthropods as well as vertebrates. These visitors arrive at specific times during the degradation of the corpse, which is influenced both by environmental conditions and by the activity of the various decomposers. Forensic entomology uses the results obtained from the study of scavenging arthropods, considered to be real biological clocks that can detect a carrion from a great distance, to solve criminal cases. It is in this sense that this work was carried out to (1) inventory the necrophagous arthropods colonizing and involved in the decomposition process of the corpses of domestic pigs packaged at different seasons/sites, (2) identify the differents stages of decomposition of the wrapped carcasses and (3) determine the post mortem intervals during the differents climatics seasons/sites in the Malombo forest in the Department of Nyong and Kéllé Central Region of Cameroon. To achieve this objective, from january to november 2018, four healthy pigs, weighing between 63 and 65 kg, two males and two females, were euthanized and then strangulated (with a rope to confirm dead and prevent any bloodshed) and each inserted, in a biodegradable body bag. These remains were deposited in a 5m x 5m quadrat surrounded by a lattice mesh screen 2cm x 2cm which can only allow arthropods colonizing the covered corpse. In high dry season (HDS) and low rainy season (LRS), necrophagous arthropod sampling, lasting approximately 1h 30 min, were carried out three times a day (8 am, 12 pm and 4 pm); However, in the low dry season (LDS) and the high rainy season (HRS), sampling was carried out twice a day (8 am and 2 pm). Sampling was conducted successively every day for 31 days and then weekly. Arthropods collected with pitfalls and pliers were fixed in 70° ethyl alcohol contained in plastic tubes and identified at possible to the specific level. Observation of physical modifications in the remains identified six stages of decomposition: fresh, bloating, advanced bloating, active decomposition, advanced decomposition and skeleton. The duration of the post-mortem interval varied over the different seasons/sites as well as the necrophagous fauna that composed them. A total of 46,082 individuals, distributed in 3 classes, 12 orders, 48 families, and 158 species/morphotypes were sampled at various stages of carrions decompositions. This arthropodofauna was represented by 29545 Diptera or 64.1%, 9231 Mesostigmata or 20.03%, 3432 Hymenoptera or 7.45%, 2403 Coleoptera or 5.2%, 370 Hemiptera or 0 72%, 307 Orthoptera or 0.67%, 304 Araneids or 0.66%, 301 Lepidoptera or 0.65%, 130 Spirostreptida or 0.28%, 61 Isoptera or 0.13%, 33 Dictyoptera or 0.0 7%, 5 Polydesmida or 0.01% of the total sample. Under an open canopy, i.e. in LRS and LDS, the decomposition of the carrions was rapid, while under a dense canopy, i.e. during the HDS and HRS, the packed corpses remained wet and their decomposition time was long. These results show that abiotic factors (temperature, environment, relative humidity and rainfall) play an important role in the decomposition of a corpse by necrophagous arthropods and determine the post-mortem interval.