Identifying blowfly species using posterior spiracle by Error-rate based morphometrics in third instar larvae

Abstract

Necrophagous flies are the first insects to colonize corpses in medicolegal cases, making the identification of their larvae species crucial for the utilization of forensic entomology data. However, morphological species identification of larvae is challenged by issues such as limited species range and difficulty. This study aimed to address the limitations of existing morphological identification methods by developing a straightforward and unified approach for identifying third instar larvae. We devised new classification indices—Angle Between Slits, Distance Between Slits, and Length BiSlits—using three pairs of posterior spiracular slits. Based on the error rate and morphometrics, we developed a classification method called Error-rate Based Morphometrics (EBM). Using the three indices and EBM, we developed a new species identification method.

This study targeted nine major species of necrophagous Calliphoridae flies found in Korea. Basic statistical data and species identification criteria for the three indices were established using a total of 151 samples from the nine species. Additionally, the accuracy of the species identification method and the significance of the three indices were statistically analyzed.

The morphological species identification method using EBM demonstrated an accuracy of 92.7% for all species. Additionally, the indices utilized for species identification were confirmed to be significant indicators with low correlation to larval development, as measured by body length.

This study developed a new species identification method using the classification indices along with EBM. The morphological species identification method for third instar larvae using EBM enable rapid species identification with high-magnification posterior spiracle images.