Cuticular hydrocarbons as pupal age markers of two species of blowflies Chrysomya (Diptera: Calliphoridae): Implications for estimating the postmortem interval.

Blowflies are important to estimate the postmortem interval (PMI), since they are the first to interact with the carcass. However, depending on the decomposition stage, only pupae can be found. A method that has currently been suggested is the use of cuticular hydrocarbons (CHCs) in forensically important fly species to aid in estimating PMI; however, studies from the pupal stage are rare. Therefore, this study aimed to test two hypotheses: (1) CHCs from fly pupae can be used as an auxiliary taxonomic tool. (2) There is significant chronological variation in composition throughout pupal development. 315 pupae were used from two fly species of different ages, being 21 pupae for each age group and using three pupae per extraction, n = 7, from which the CHCs were extracted every hour, from the first hour to the tenth; then, samples were collected every 24 h until adult emergence. We found that in the cuticle of Chrysomya albiceps and Chrysomya megacephala, pupae detected 19 and 23 compounds, respectively, identified as linear alkanes, branched alkanes, and alkenes. According to the results, CHCs of the pupae vary significantly between the species and throughout their development, with compounds that are specific to the initial hours and others to the final hours. We can conclude that our results are promising for use in forensics, as changes in intra-pupal development result in a characteristic chemical profile throughout the ages analyzed, therefore helping criminal experts in estimating the PMI.