Puparial case hydrocarbons of Chrysomya megacephala as an indicator of the postmortem interval

The puparial case is one of the most common ‘stages’ of necrophagous flies encountered in crime investigations of highly decomposed corpses. If methods for determining the weathering time of these puparial cases are developed, it is possible that the postmortem interval (PMI) could be estimated accordingly. Gas chromatography coupled with mass spectrometry (GC–MS) was used to determine the changes with the weathering time in cuticular hydrocarbons of the puparial cases of Chrysomya megacephala in the laboratory. The results have shown that cuticular hydrocarbons of the puparial cases were a mixture of n-alkanes, methyl-branched alkanes, and dimethyl-branched alkanes. The carbon chain length ranged from C21 to C35, and the hydrocarbon composition showed significant regular changes with the weathering time. For the even numbered n-alkanes with low molecular weight, namely n-C22, n-C24 and n-C26, the abundance increased significantly with the weathering time. For n-C26, in particular, a linear increase in abundance with the weathering time was observed. In addition, for most of the other low molecular weight hydrocarbons (n-C26 or below), the abundance decreased significantly with the weathering time. It is concluded that, cuticular hydrocarbon is a potential indicator of the weathering time in C. megacephala, and possibly in other necrophagous flies, and might further be used to determine the PMI.