Age estimation of Phormia regina pupae based on ATR-FTIR and chemometrics.

Ruonan Zhang, Yundi Gao, Gengwang Hu, Yinghui Wang, Liangliang Li, Yi Guo, Shipeng Shao, Siqi Liu, Yu Wang
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Abstract

Accurate postmortem interval estimation is vital in the investigation of homicides, suicides, and accidental deaths. It is key in narrowing suspect lists, improving crime-solving efficiency, and offering solace to bereaved families. The intra-puparial period, comprising about half of a fly's developmental cycle, presents challenges for morphological age estimation. External changes are limited to color shifts and the appearance of respiratory horns on the puparium only within several hours after pupariation, while detailed internal development analysis often requires invasive methods like removing the puparium, which can be damaging. Additionally, these techniques usually depend on a forensic entomologist's expertise, which lead to subjective biases. This study employed attenuated total reflection-fourier transform infrared spectroscopy, a rapid, non-destructive method for analyzing proteins, chitosan, and chitin in puparia. Data showed a consistent reduction in the concentration of the amide I band within the puparium during the intra-puparial development at five constant temperatures (19 °C, 22 °C, 25 °C, 28 °C and 31 °C). This trend in the spectral data effectively distinguishes pupae at various stages of intra-puparial development, facilitating precise age estimation, which is critical for the estimation of the minimum postmortem interval (PMImin). Finally, this work combined the total reflection-fourier transform infrared spectroscopy with chemometric analysis and successfully developed a partial least squares discriminant analysis model and a random forest model, with accuracies of 88 % and 81 %, respectively. These models enable the non-invasive age estimation of P. regina in its intra-puparial period, a stage traditionally difficult to assess morphologically, thus laying the groundwork for PMImin estimation using fly pupae.

基于 ATR-FTIR 和化学计量学估算 Phormia regina 蛹的年龄。
准确的死后间隔估计对于调查凶杀、自杀和意外死亡至关重要。它是缩小嫌疑犯名单、提高破案效率和抚慰死者家属的关键。育雏期约占苍蝇发育周期的一半,对形态年龄的估计提出了挑战。外部变化仅限于蛹化后几小时内的颜色变化和蛹体上呼吸角的出现,而详细的内部发育分析往往需要采用侵入性方法,如取下蛹体,这可能会造成损害。此外,这些技术通常依赖于法医昆虫学家的专业知识,从而导致主观偏见。这项研究采用了衰减全反射-傅立叶变换红外光谱法,这是一种快速、非破坏性的方法,用于分析蛹体内的蛋白质、壳聚糖和甲壳素。数据显示,在五个恒定温度(19 °C、22 °C、25 °C、28 °C和 31 °C)下,蛹体内酰胺 I 波段的浓度在蛹内发育过程中持续降低。光谱数据中的这一趋势可有效区分蛹体内不同发育阶段的蛹,有助于精确估计蛹的年龄,这对估计最小死后间隔(PMImin)至关重要。最后,这项研究将全反射-傅立叶变换红外光谱与化学计量分析相结合,成功地建立了偏最小二乘判别分析模型和随机森林模型,准确率分别为 88% 和 81%。这些模型能够在传统上很难从形态学角度评估的蛹内期对 P. regina 进行无创年龄估计,从而为利用蝇蛹估计 PMImin 奠定了基础。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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