Temperature-dependent development of Musca domestica (Diptera: Muscidae) and posterior spiracle-based substaging of third instar larvae.

Estimating the minimum postmortem interval (mPMI) is an essential task in practical forensic entomology. mPMI estimation is carried out using information on the species recovered at the scene, appropriate developmental data, and the developmental stages of those species. In this study, we obtained developmental data for Musca domestica Linnaeus, 1758 (Diptera: Muscidae), a synanthropic species that inhabits human-associated environments and is also encountered in forensic entomology cases. Musca domestica was reared at constant temperatures ranging from 16 to 34 °C, and we generated developmental data, estimated a thermal summation model, and subdivided third instar development based on time-dependent changes in the posterior spiracle. Musca domestica completed development across all tested temperatures (706.5 h at 16 °C; 163.6 h at 34 °C). For the entire developmental period, the lower developmental threshold and total thermal requirement were estimated as 11.43 °C and 3350.2 accumulated degree hours, respectively. We also documented time-dependent changes in third instar posterior spiracle structures-the peritreme, spiracular plate, slits, and scar-and proposed developmental substages centered on the scar and surrounding morphology. The third instar was subdivided into four substages based on externally observable features of these structures. Through this work, we provide developmental data for Korean populations of the forensically important species M. domestica and propose third instar substages that enable more precise estimation of developmental time and can be applied using simple microscopic observations in forensic casework.