Degradation dynamics of cuticular hydrocarbons of empty puparia in forensically important blow fly Lucilia sericata in soil and under room conditions: Insights and machine learning applications

Abstract

Empty puparia, remnants of blow fly larvae cuticles, aid in estimating long-term post-mortem intervals. Assessing alterations in cuticular hydrocarbons (CHCs) composition provides insights into environmental effects on their degradation, enabling age estimation methods for empty puparia found at the crime scene. The current study aimed to investigate the temporal variations of five predominant CHCs of empty puparia of Lucilia sericata (Diptera: Calliphoridae). The study was conducted over six months (180 days) under controlled conditions, comparing the storage of puparia in soil and non-soil pupation medium (room conditions). The five CHCs investigated are- n-pentacosane, n-hexacosane, n-heptacosane, n-octacosane, and n-nonacosane. Gas chromatography-mass spectrometry (GC–MS) was used to analyze the cuticular hydrocarbons after they were extracted in hexane. The findings indicated that the degradation rate of CHCs was influenced by the surrounding environment, with more rapid degradation observed in soil conditions compared to room conditions. This suggests that soil can impact the weathering process of empty puparial cases. To predict the age of the puparial cases, a Support Vector Machine (SVM) analysis was conducted based on the concentrations of hydrocarbons. The SVM models demonstrated promising performance in age prediction, exhibiting high R-squared values and low prediction errors. By highlighting the influence of environmental factors on CHC degradation and demonstrating the efficacy of SVM models in age prediction, this study lays the groundwork for further exploration and development of CHCs as valuable tools in forensic and ecological research.