Thümmel Luise, Tintner-Olifiers Johannes, Amendt Jens
Goethe-University Frankfurt, University Hospital, Institute of Legal Medicine, Frankfurt am Main, Germany.
Department of Aquatic Ecotoxicology, Faculty of Biological Sciences, Goethe University, Frankfurt am Main, Germany.
Med Vet Entomol. 2025 Mar;39(1):22-32. doi: 10.1111/mve.12748. Epub 2024 Aug 2.
Estimating the age of immature blow flies is of great importance for forensic entomology. However, no gold-standard technique for an accurate determination of the intra-puparial age has yet been established. Fourier transform infrared (FTIR) spectroscopy is a method to (bio-)chemically characterise material based on the absorbance of electromagnetic energy by functional groups of molecules. In recent years, it also has become a powerful tool in forensic and life sciences, as it is a fast and cost-effective way to characterise all kinds of material and biological traces. This study is the first to collect developmental reference data on the changes in absorption spectra during the intra-puparial period of the forensically important blow fly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae). Calliphora vicina was reared at constant 20°C and 25°C and specimens were killed every other day throughout their intra-puparial development. In order to investigate which part yields the highest detectable differences in absorption spectra throughout the intra-puparial development, each specimen was divided into two different subsamples: the pupal body and the former cuticle of the third instar, that is, the puparium. Absorption spectra were collected with a FTIR spectrometer coupled to an attenuated total reflection (ATR) unit. Classification accuracies of different wavenumber regions with two machine learning models, i.e., random forests (RF) and support vector machines (SVMs), were tested. The best age predictions for both temperature settings and machine learning models were obtained by using the full spectral range from 3700 to 600 cm. While SVMs resulted in better accuracies for C. vicina reared at 20°C, RFs performed almost as good as SVMs for data obtained from 25°C. In terms of sample type, the pupal body gave smoother spectra and usually better classification accuracies than the puparia. This study shows that FTIR spectroscopy is a promising technique in forensic entomology to support the estimation of the minimum post-mortem interval (PMI), by estimating the age of a given insect specimen.
估算未成熟丽蝇的年龄对于法医昆虫学至关重要。然而，目前尚未建立用于准确确定蛹内年龄的金标准技术。傅里叶变换红外（FTIR）光谱法是一种基于分子官能团对电磁能量的吸收来对材料进行（生物）化学表征的方法。近年来，它也已成为法医和生命科学中的一种强大工具，因为它是一种快速且经济高效地表征各种材料和生物痕迹的方法。本研究首次收集了法医重要丽蝇红头丽蝇（双翅目：丽蝇科）蛹内发育期间吸收光谱变化的发育参考数据。将红头丽蝇在20°C和25°C的恒定温度下饲养，在其整个蛹内发育过程中每隔一天处死一批样本。为了研究在整个蛹内发育过程中哪个部分在吸收光谱上产生的可检测差异最大，每个样本被分成两个不同的子样本：蛹体和三龄幼虫的前表皮，即蛹壳。使用与衰减全反射（ATR）单元耦合的FTIR光谱仪收集吸收光谱。用随机森林（RF）和支持向量机（SVM）这两种机器学习模型测试了不同波数区域的分类准确率。对于两种温度设置和机器学习模型，通过使用3700至600 cm的全光谱范围获得了最佳年龄预测。虽然SVM对在20°C饲养的红头丽蝇准确率更高，但对于在25°C获得的数据，RF的表现几乎与SVM一样好。就样本类型而言，蛹体的光谱更平滑，分类准确率通常也比蛹壳更好。这项研究表明，FTIR光谱法在法医昆虫学中是一种很有前景的技术，可通过估计给定昆虫样本的年龄来支持最低死后间隔时间（PMI）的估算。
