New application of ATR-FTIR spectroscopy for postmortem interval estimation based on puparia of the sarcosaprophagous fly Chrysomya megacephala (Diptera: Calliphoridae)

Postmortem interval (PMI) estimation remains a challenge in forensic science due to the lack of efficient methods. In recent years, the preadult development of sarcosaprophagous flies has been recognized as a reliable method to estimate the minimum postmortem interval (PMImin). However, this method may fail once the PMI exceeds the duration of preadult development (i.e. after eclosion), leaving puparia of sarcosaprophagous flies as the only evidence for the estimation of the PMI at the crime scene. Fourier transform infrared (FTIR) spec-troscopy with attenuated total reflectance (ATR) accessory was used in this study to collect comprehensive biochemical information from puparia of the sarcosaprophagous fly Chrysomya megacephala (Fabricius) (Diptera, Calliphoridae) at different time after eclosion (TAE). We established the partial least square (PLS) regression model using the acquired spectral dataset. The prediction results of the PLS regression model showed that R2CV of the internal cross-validation (calibration dataset) was 0.864 with RMSECV = 3.711 d and R2P of the prediction dataset was 0.909 with RMSEP = 3.045 d. The RMSEP/RMSECV value was 0.82 in our PLS regression model. Our results indicate that the TAE of puparia are highly predictable, which is valuable for the estimation of long-term PMImin.