Ultrastructure of male terminalia of Boettcherisca peregrina and Boettcherisca nathani (Diptera: Sarcophagidae), flesh fly species of forensic importance

Abstract

Flesh flies are received greater attention due to their use as evidence in forensic investigations of decomposing human remains. Investigators will often use age of immature insects associated with such remains as the minimal postmortem interval (PMImin) given certain assumptions. Boettcherisca peregrina is a significant flesh fly species of forensic importance in several countries, whereas B. nathani is potentially a species of forensic importance. Distinguishing these two species is difficult and relies on close examination of the male terminalia. For genus Boettcherisca belonging to subfamily Sarcophaginae, identification is primarily based on the morphological structures associated with male terminalia. Using light microscopy and scanning electron microscopy, similarities and differences were determined for these two species. In this study, B. peregrina was collected from an urban area of Mueang District, while B. nathani was collected from the highland forest area of Doi Saket District, Chiang Mai province, northern Thailand. The morphological observations indicated similarities in the morphology of vesica (large, rounded anterior margin, bi-lobed, half upper-outer margins serrated), harpes (well-developed, elongated, broad basally with bifurcated apically) and lateral styli (two parallel tube-like with open ends with microserration apically) in both species. However, differences were found with the cercus and juxta. With regards to the cercus, B. peregrina has bristles or setae only along the posterior surface and the cercal tip is pointed, while B. nathani has bristles or setae on both the anterior and posterior surfaces, and the cercal tip is hook-shaped. Morphometric measurements of three criteria of the cerci (length from top to middle, internal distance at narrow part and distance between apex of cercal prong) revealed that the average length of each criteria of B. nathani cerci (n = 30) were significantly greater than B. peregrina cerci (n = 30). As for the juxta, the juxtal lateral plate was different: primarily bifurcated in B. peregrina and non-bifurcated in B. nathani. The medial part of juxta was different: V-shaped 95.8% (46/48) and, to a lesser extent, W-shaped 4.2% (2/48) in B. peregrina, only W-shaped 100% (52/52) in B. nathani. Such information is useful for entomologists to distinguish between adult males of these two species, which could be valuable when determining colonization patterns in association with decomposing human remains.