# A Preliminary Study on Species Identification of Immature Necrophagous Phorid Flies Based on FTIR Spectroscopy

## TL;DR

This study shows how FTIR spectroscopy can quickly identify immature phorid fly species used in forensic investigations.

## Contribution

The study introduces FTIR spectroscopy with chemometric analysis for rapid species identification of immature phorid flies in forensic entomology.

## Key findings

- FTIR spectra in the fingerprint region (1800–900 cm−1) showed distinct absorption peak intensities among three phorid fly species.
- PLS-DA analysis successfully distinguished the three species at the same developmental stage.
- The method allows for rapid species identification and age estimation of immature phorid flies.

## Abstract

Accurate identification of the insect species is the initial step in forensic entomology case analysis. Phorid flies are significant forensic insects found on indoor and buried corpses. Due to their minute size, species identification of their immature stages presents certain challenges. This study utilized Fourier transform infrared (FTIR) combined with multivariate analytical methods to identify three common species of necrophagous phorid fly immatures. The research demonstrated that using spectral data from the fingerprint region (1800–900 cm−1) coupled with partial least squares-discriminant analysis (PLS-DA) effectively discriminates the species. This study provides an effective tool for the rapid identification of immature species in forensic entomology.

Phorid flies serve as the main colonizers of human remains in both indoor and burial environments. Their developmental patterns can be utilized to estimate the minimum postmortem interval (minPMI). Accurate species identification, particularly for immature stages, is essential before utilizing their developmental data to estimate minPMI. This study employed Fourier transform infrared spectroscopy (FTIR) coupled with principal components analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) to investigate species identification of eggs (0 h, 8 h, 16 h), larvae (12 h, 60 h, 84 h), and pupae (1 d, 5 d, 10 d) of three necrophagous Phoridae species, Dohrniphora cornuta, Diplonevra funebris, and Megaselia scalaris at 24 °C. The results showed that the FTIR spectra within the fingerprint region (1800–900 cm−1) differed among the three immature phorid flies. These differences were primarily manifested in absorption peak intensities. The PLS-DA analysis successfully distinguished the three species at the same developmental stage. This study demonstrated the feasibility of utilizing FTIR spectroscopy coupled with chemometric methods to both rapidly identify the species of immature small flies and simultaneously estimate their age.