Chrysomya chani Kurahashi (Diptera: Calliphoridae), a blow fly species of forensic importance: morphological characters of the third larval instar and a case report from Thailand

Abstract

Blow flies are worldwide the most important insects from a forensic point of view. In Thailand, aside from the two most common species, Chrysomya megacephala (F.) and Chrysomya rufifacies (Macquart), Chrysomya chani Kurahashi was also found to be of forensic importance. We present a case of a human female cadaver in its bloated stage of decomposition, discovered at Pachangnoi Subdistrict, northern Thailand. Entomological sampling during the autopsy displayed an assemblage of numerous dipteran larvae. Macroscopic observations showed the coexistence of third instar larvae of the three blow flies C. megacephala, Chrysomya villeneuvi Patton, an unknown blow fly species and one muscid, Hydrotaea sp. The minimum post-mortem interval was estimated to be six days, based on the developmental rate of C. megacephala. The ID of the unknown larva, which is the focus of this report, was revealed later as C. chani by DNA sequencing, using a 1205 bp of cytochrome c oxidase subunit I (COI). The occurrence of C. chani on a human body revealed the need to analyse and describe the morphology of its immature stage, to enable forensic entomologists to identify this fly species in future cases. The morphological examination of the third instar was performed, revealing peculiar characteristics: protuberant tubercles encircling abdominal segments; 9-11 lobes on the anterior spiracle; six prominent pairs of tubercles along the peripheral rim of the eighth abdominal segment; a heavily sclerotized complete peritreme of the posterior spiracles. A key to differentiate the third instar of blow flies of forensic importance in Thailand is provided.

Keywords: Chrysomya chani; Forensic science; Thailand; forensic entomology; larval morphology, identification.

Figure 1.

Map of Thailand showing the collection site where the human remains discovered, at Pachangnoi Subdistrict (N 19°19′24.24″; E 100°27′17.28″), Pong District, Phayao Province (green dot), northern Thailand.

Figure 2.

Light micrographs of third instar larvae of Chrysomya chani. (A) Whole body, dorsal view. (B) Anterior end showing the prominent spine bands between the second and third thoracic segments (arrowhead), and prominent tubercles encircling the body, initiating from the first abdominal segment (arrow) and denticles at the surface integument (red arrow). (C) Posterior end showing prominent tubercles encircling the body and a pair of posterior spiracle.

Figure 3.

Light micrographs of third instar larvae of Chrysomya chani. (A) Whole body, lateral view; anterior end at left, posterior end at right. Arrows indicate the initial protuberant tubercles encircling body segments at the first abdominal segment (arrow). (B) Anterior end showing cephaloskeleton (c), anterior spiracle (a) and spine bands (s) between the first and second thoracic segments. Anterior spiracle consisted of 9–11 papillae arranging in a single row. Arrow displays surface integument, covering with dense variable size of denticles. (C) Higher magnification of the cephaloskeleton and anterior spiracle (a). Arrows indicate window of ventral cornua. Abbreviation of cephaloskeleton: as, accessory sclerite; db, dorsal bridge; dc, dorsal cornua; den, dental sclerite; is, intermediate sclerite; mh, mouthhooks; pb, parastomal bar; vc, ventral cornua; vp, vertical plate. (D) Posterior view of the eighth abdominal segment showing prominent six pairs of tubercles along the peripheral rim. Posterior spiracle (ps) is apparent. Abbreviation of tubercles: IDT, inner dorsal tubercles; MDT, median dorsal tubercles; ODT, outer dorsal tubercles; OVT, outer ventral tubercles; MVT, median ventral tubercles; IVT, inner ventral tubercles. (E) Posterior view of the eighth abdominal segment showing remarkably sculpture encircling the posterior spiracles (ps) and adjacent to these tubercles (arrow). (F) Higher magnification of posterior spiracles displaying thick, heavily sclerotize complete posterior spiracular peritreme (p) enclosing three spiracular slits. Arrow indicates indistinct button (or ecdysial scar).

Figure 4.

Light micrographs of third instar larva of Chrysomya villeneuvi and Lucilia cuprina. (A) Third instar larva of C. villeneuvi showing large, elongate tubercles on the abdominal segments. (B) Third instar larva of L. cuprina showing smooth abdominal segments.

Figure 5.

Light micrographs of larva of Chrysomya rufifacies and Chrysomya villeneuvi. (A) Third instar larva of C. rufifacies showing large, elongate tubercles on the abdominal segments. (B) Tubercle of C. rufifacies larva bears numerous small spines at tip. (C) Posterior spiracle of C. rufifacies showing large, heavily sclerotized incomplete peritreme. (D) Tubercle of C. villeneuvi larva bears numerous small spines throughout. (E) Posterior spiracle of C. villeneuvi larva showing large, heavily sclerotized incomplete peritreme.

Figure 6.

Third instar larva of Chrysomya nigripes. (A) Posterior spiracle showing gradually enlarged of end of upper peritreme (arrow). (B) Spines between the first and second thoracic segment. (C) A specimen with brown patch on dorsal integument (arrow). (D) A specimen without brown patch of dorsal integument.

Figure 7.

Light micrographs of larva of Chrysomya bezziana and Chrysomya megacephala. (A) Posterior spiracle of larva of C. bezziana. (B) Spines between the first and second thoracic segment of C. bezziana. (C) Posterior spiracle of larvae of C. megacephala. (D) Spines between the first and second thoracic segment of larvae of C. megacephala.

Figure 8.

Light micrographs of larva of Lucilia sinensis, Lucilia cuprina and Lucilia porphyrina. (A–C) Larva of L. sinensis. (A) Posterior spiracle. (B) Spines between the first and second thoracic segment. (C) Cephaloskeleton showing accessory sclerite (arrow). (D–F) Larva of L. cuprina. (D) Posterior spiracle. (E) Spines between the first and second thoracic segment. (F) Cephaloskeleton. (G–I) Larva of L. porphyrina. (G) Posterior spiracle. (H) Spines between the first and second thoracic segment. (I) Cephaloskeleton.

Figure 9.

Neighbour-joining tree based on COI gene (1 205 bp) of Chrysomya chani collected from the human remain from Thailand (pink dot) and other blow fly species. Voucher codes or accession number are presented in parentheses. Bootstrap values (>50%) were shown nearby the node of the trees.