Interval Estimation of Thermal Summation Parametersin Forensically Important Insects

Estimating time of death based on entomological evidence commonly relies on the "law of total effective temperature", which requires developmental parameters of specific insect taxa. These are often calculated using the method of Ikemoto and Takai. However, this approach has key limitations. It assumes a homogeneous population and does not provide meaningful interval estimates, despite substantial variation within species and even populations. Moreover, by aggregating raw data before analysis, it discards valuable information, potentially reducing accuracy. In this study, we propose an alternative method that addresses both issues. It estimates interval values for developmental parameters while simultaneously identifying component populations within a dataset. The method involves fitting a finite mixture of Weibull distributions to development time data using the Expectation-Maximization (EM) algorithm. This allows for the inclusion of individual-level variability in the estimation process. We tested the method using previously published developmental data on two forensic beetle species, Creophilus maxillosus and Necrodes littoralis (Staphylinidae). Our approach yielded 95% intervals with coverage close to the nominal level, in contrast to Ikemoto and Takai’s method, which captured only 75% and 59% of actual cases, respectively. These findings suggest that our method improves the reliability of insect-based postmortem interval estimates in forensic entomology.