Abstract: 【Aim】 This study aims to examine the changing trend of puparium color of a common necrophagous fly (Lucilia sericata) under different constant temperatures and to prepare the standard color plates based on the RGB values of puparium, so as to provide a scientific support for the estimation of the postmortem interval (PMI) in forensic medicine. 【Methods】 Ten pupae of L. sericata were sampled at 12 h intervals from prepupa to emergence under different constant temperatures (16℃, 20℃, 24℃, 28℃ and 32℃). The variation of puparium color at all the observed time points in the pupal stage of L. sericata was observed and photographed. The corresponding RGB values of puparium color were collected and analyzed by digital image processing system to prepare the standard color plates. Multivariate regression analysis was employed for fitting the relationship between the developmental time of pupa and the R value of the RGB values of puparium color by R software. 【Results】 The puparium color of L. sericata gradually deepened with the developmental time under different constant temperatures, and obvious changes were observed at the beginning and final time of the pupal stage. Based on the RGB values at different developmental time, five standard color plates of L. sericata puparium were prepared corresponding to different constant temperatures. 【Conclusion】 At the crime scene, the standard color plates of puparium obtained in this study can be used to preliminarily estimate the pupal stage through visual comparison as an auxiliary method. Based on this estimation, the PMI can be deduced.

Key words: Lucilia sericata; temperature, puparium color, standard color plates, RGB value, PMI