Succession study on forensically important beetles on carcasses aids in determining the PMI

Paper ID: 584Presentation name: Succession study on forensically important beetles on carcasses aids in determining the PMIPresentation date: Friday 24 November 2023Presentation start time: 12:30:00 PMPoster terminal: 3 For this study, decomposing domestic buffalo carcasses in agricultural fields were used as ecological models to document the succession and population dynamics of forensically important Histeridae beetles under natural conditions and to relate their abundance and diversity to decomposition stage and key environmental variables (soil pH, temperature, relative humidity, and season).Study design and carcass setupEach trial used a single adult buffalo carcass placed at a farmland carcass‑disposal point, with six carcasses studied across different seasons (monsoon, summer, autumn, and winter) to capture seasonal variation in Histeridae assemblages. Carcasses were left to decompose undisturbed from the fresh stage through the bloated, active decay, advanced decay, and remains/skeletal phases, and each carcass was monitored daily until the residual stage was reached.Beetle sampling methodologyA strategic transect‑style search pattern was used around each carcass to ensure complete coverage of the carcass surface and the underlying/adjacent soil. During peak beetle activity periods (09:00–11:00 h and 14:00–17:00 h), Histeridae were collected manually on every visit using forceps and aspirators from the carcass, body orifices, maggot masses, and soil immediately beneath and around the carcass. All Histeridae specimens from a given visit were pooled per carcass, labelled with date, carcass ID, decomposition stage, and microhabitat (on carcass vs. soil), preserved, and later identified to species.Environmental measurementsAt each visit, ambient air temperature, carcass surface temperature, and beneath‑carcass temperature were measured on site using a Kestrel 2500 portable weather meter, and relative humidity was recorded with a portable hygrometer at the carcass location. Additional humidity data for the study period were obtained from meteorological departments to characterize broader climatic conditions during each decomposition sequence.For soil pH, approximately 20 g of soil were collected from beneath and around each carcass, air-dried, and transferred to a clean bottle, to which 40 ml of water were added following FAO/GSP guidelines. The suspension was vigorously shaken for one minute and allowed to settle for 20–30 minutes, and the pH was then measured in the supernatant using a calibrated conductivity/pH meter with electrodes immersed in the clear solution.Decomposition staging and insect contextThe decomposition stage was assigned using standard forensic entomology criteria (fresh, bloated, active decay, advanced decay, and remains), supported by the presence and development of blowfly stages following Haskell et al. (1997) (oviposition, egg, larval instars I–III, post‑feeding larva, puparium, and adult emergence). This allowed the temporal patterns of Histeridae arrival and peak abundance to be interpreted relative to blowfly maggot colonization and cadaveric volatile organic compound release during active and advanced decay.Specimen processing and analysisAcross all carcasses and seasons, a total of 5,281 Histeridae specimens were collected and examined for morphological and ecological analysis. Specimens were sorted to morphospecies and identified to species level where possible (e.g., Saprinus splendens, S. caerulescens, S. optabilis, S. quadriguttatus, Atholus daldorffi, Merohister jakeli, and Hypocacculus sp.), with some individuals retained as unidentified Histeridae pending further taxonomic work. For each carcass, daily counts of each species were tabulated, allowing construction of succession curves showing arrival time, peak abundance, and decline across decomposition stages and across the 7–30 day observation windows of different trials.Data analysis and interpretationTemporal trends were analyzed by plotting species‑wise and total Histeridae abundance over days post‑exposure and decomposition stage for each carcass, with particular attention to exponential increases during active decay, peak abundance after the bloated stage, and subsequent decline towards the remains stage. Relationships between Histeridae abundance/diversity and soil pH were explored by comparing beetle counts against measured pH values; maximum biodiversity was observed near soil pH 5.8 under carcasses. Seasonal effects were interpreted descriptively: summer (25–45°C) showed the highest Histeridae diversity and activity, monsoon (28–35°C) also exhibited elevated activity due to accelerated decomposition, while winter (7–20°C) and late autumn showed reduced activity and fewer species.Ethical and legal contextCarcasses used were naturally available buffaloes disposed at designated farmland carcass‑disposal points, and no animals were killed specifically for this research. Sampling was non‑destructive with respect to vertebrate remains and conformed to typical forensic entomology field‑collection practices; institutional permission and logistical support were provided by Panjab University, Chandigarh, for fieldwork and laboratory processing.