Cuticular hydrocarbon of pupal cases of Chrysomya megacephala (fabricius) and its possible use for estimating postmortem interval

Abstract

Although the pupal cases of Chrysomya megacephala have been commonly observed at crime scenes, its utilization for forensic investigation remains nascent. Despite several studies reporting about the use of cuticular hydrocarbons (CHCs) for estimating the age of pupal cases, they were either conducted in laboratory controlled experiments or in environmental conditions peculiar to Malaysia. Hence, this present research that examined the CHCs compositions in the pupal cases of C. megacephala exposed to the natural weathering process in Malaysia (up to 14 days) for providing empirical evidence for age estimation deserves forensic consideration. While confirmation of the identity of CHCs was done using Gas Chromatography- Mass Spectrometer (GC-MS), Gas Chromatography- Flame Ionization Detector (GC-FID) was used for quantifying the concentrations. Results revealed that the analysis of the hexane extract of the pupal cases of C. megacephala contained a mixture of odd-numbered high molecular weight aliphatic (i.e. heptacosane (n-C27) and nonacosane (n-C29)) and branched alkanes (i.e. tetradecane, 2, 6, 20-trimethyl- and octadecane, 3-ethyl-5-(2-ethylbutyl)). Significant decrease (P <0.05) in the concentrations of n-C27 and n-C29 was observed, with the pattern of the decrease being highly correlated (r > -0.926) with that of the three subsequent weathering intervals. Such findings had enabled formulation of credible mathematical algorithms for relating the concentrations of n-C27 and n-C29 in the pupal cases of C. megacephala versus the natural weathering intervals, a possible means for estimating the age of such pupal cases. Therefore, the findings have to be duly considered whenever interpretations of the pupal cases need to be relied upon in crime situations with similar environmental conditions.