Seasonal study of the decomposition pattern and insects on a submerged pig cadaver

Abstract

Research on studying the decomposition pattern in aquatic habitat is very sparse worldwide. Due to this void, assessment of the postmortem submersion interval (PMSI) of drowned and submerged cadavers is still inaccurate and imprecise. The current work focused on studying the decomposition pattern and insects associated with submerged pig (Sus scrofa) carcasses during various seasons (winter, spring, summer, and rainy) for two years. The total postmortem submersion interval (PMSI) from the fresh stage till the sunken remains stage varied from 25 days for rainy season (624.5 ADD) to 78 days (1890.5 ADD) for winter season. The spring season at 44 days (1067.5 ADD) and summer season at 31 days (763.5 ADD) had moderate PMSI. During this time interval, five stages of decomposition were studied: submerged fresh, early floating, floating decay, advanced floating decay, and sunken remains. A total of 2385 insect specimens were found to be associated with different decomposition stages. The terrestrial activity during the first stage (submerged fresh) was almost nil as the carcasses were submerged. During the early floating stage (2nd stage), various terrestrial insect species visited the carcass and laid their eggs. Aquatic insects belonging to Chironomidae (Diptera), Coenagrionidae, Lestidae, Aeshnidae, Gomphidae and Libellulidae (Odonata) were also found associated with this stage. In the floating decay (3rd stage), the insects visiting and colonizing the carcass were the same as in the second stage along with Calliphoridae and Sarcophagidae (Diptera). Species from the group of scavenging aquatic beetles i.e. Enochrus esuriens (Walker, 1858), Regimbartia attenuata (Fabricius, 1801), Helochares sp. (Family: Hydrophilidae) and burrowing water beetles, Canthydrus laetabilis (Walker, 1858) (Family: Noteridae) and some terrestrial species of beetles, i.e. Saprinus sp., Saprinus pensylvanicus (Hatch, 1929) (Family: Histeridae), Necrobia rufipes (De Geer, 1775) (Family: Cleridae) were also present during the 3rd, 4th and 5th stages. During advanced floating decay (4th stage) and sunken remains (5th stage), many hemipteran species such as Ranatra digitata (Hafiz and Pradhan, 1949), Ranatra filiformis (Fabricius, 1790) along with many coleopterans were found visiting the corpse.