Estimation of postmortem interval (PMI) based on empty puparia of Phormia regina (Meigen) (Diptera: Calliphoridae) and third larval stage of Necrodes littoralis (L.) (Coleoptera: Silphidae) - Advantages of using different PMI indicators

Abstract

On 16 July 2015, a body of a 64-year-old man in advanced decomposition was found in an open area of the suburb of Śrem (western Poland). Postmortem interval (PMI) was estimated by forensic pathologist for 3-6 weeks. Insects were sampled from the cadaver and the soil from below the cadaver. Empty puparia of Phormia regina were the most developmentally advanced specimens of blowflies. Moreover, third instar larva of Necrodes littoralis was collected directly from the cadaver. For the estimation of minimum PMI from puparia of P. regina, thermal summation method was used to estimate the total immature development interval of this species. In the case of larval N. littoralis, the pre-appearance interval (PAI) was estimated using temperature method and the development interval (DI) using thermal summation method. Average daily temperatures from the nearby weather station were used, as well as the weather station temperatures corrected by 1 °C and 2 °C. The estimates were as follows: 36-38 days using empty puparia of P. regina and 37-40 days using larva of N. littoralis (for the uncorrected temperatures), 31-34 days using both P. regina and N. littoralis (temperatures corrected by +1 °C), 24-27 days using P. regina and 28-29 days using N. littoralis (temperatures corrected by +2 °C). It was concluded that death occurred 24-40 days before the body was found and most probably 24-34 days before the body was found. This is the first report when PMI was approximated by the age estimates combined with the PAI estimates. Moreover, the case demonstrates the advantages of using different entomological indicators and an urgent need for the more robust developmental model for N. littoralis, as it proved to be highly useful for the estimation of PMI.

Keywords: Forensic entomology; Forensic science; Necrodes littoralis; Phormia regina; Post-mortem interval; Pre-appearance interval.