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BackgroundChrysomya megacephala is a blow fly species of medical and forensic importance worldwide. Understanding its bionomics is essential for both designing effective fly control programs and its use in forensic investigations.MethodsThe daily flight activity, seasonal abundance related to abiotic factors (temperature, relative humidity and rainfall) and reproductive potential of this species was investigated. Adult flies were sampled twice a month for one year from July 2013 to June 2014 in three different ecotypes (forest area, longan orchard and palm plantation) of Chiang Mai Province, northern Thailand, using semi-automatic funnel traps. One-day tainted beef offal was used as bait.ResultsA total of 88,273 flies were sampled, of which 82,800 flies (93.8%) were caught during the day (from 06:00 to 18:00 h); while 5473 flies (6.2%) were caught at night (from 18:00 to 06:00 h). Concurrently, the abundance of C. megacephala was higher in the forest area (n = 31,873; 36.1%) and palm plantation (n = 31,347; 35.5%), compared to the longan orchard (n = 25,053; 28.4%). The number of females was significantly higher than that of males, exhibiting a female to male sex ratio of 2.36:1. Seasonal fluctuation revealed the highest abundance of C. megacephala in summer, but low numbers in the rainy season and winter. Fly density was significantly positively correlated with temperature, but negatively correlated with relative humidity. No correlation between numbers of C. megacephala with rainfall was found. Activity occurred throughout the daytime with high numbers from 06:00 to 18:00 h in summer and 12:00 to 18:00 h in the rainy season and winter. As for the nocturnal flight activity, a small number of flies were collected in summer and the rainy season, while none were collected in the winter. Dissection of the females indicated that fecundity was highest during the rainy season, followed by winter and summer.ConclusionsSince the assessment of daily, seasonal activity and the reproductive potential of C. megacephala remains a crucial point to be elucidated, this extensive study offers insights into bionomics, which may be considered for integrated fly control strategies and forensic entomology issues.

This is the first study to report Chrysomya pinguis (Walker) and Lucilia porphyrina (Walker) (Diptera: Calliphoridae) as forensically important blow fly species from human cadavers in Thailand, in addition to Chrysomya villeneuvi (Patton) already known in Thailand. In 2016, a fully decomposed body of an unknown adult male was discovered in a high mountainous forest during winter in Chiang Mai province. The remains were infested heavily with thousands of blow fly larvae feeding simultaneously on them. Morphological identification of adults reared from the larvae, and molecular analysis based on sequencing of 1,247 bp partial mitochondrial cytochrome c oxidase subunit 1 gene (CO1) of the larvae and puparia, confirmed the above mentioned 3 species. The approving forensic fly evidence by molecular approach was described for the first time in Thailand. Moreover, neighbor-joining phylogenetic analysis of the CO1 was performed to compare the relatedness of the species, thereby affirming the accuracy of identification. As species of entomofauna varies among cases in different geographic and climatic circumstances, C. pinguis and L. porphyrina were added to the list of Thai forensic entomology caseworks, including colonizers of human remains in open, high mountainous areas during winter. Further research should focus on these 3 species, for which no developmental data are currently available.

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The collection of Sarcophagidae made by the first author during the surveys on flies of medical and forensic importance in Thailand from 2012 to 2016 is dealt with. A total 31 genera and 86 species of the flesh flies are listed. One new genus Komisca gen. nov. is established for Sarcophaga (s. lat.) nanensis Chaiwang, Sukontason & Sukontason, 2009. One little known species, Burmanomyia aureomarginata (Shinonaga & Tumrasvin, 1979) n. com., is redescribed and illustrated. Revised identification keys to the species of Thai Sarcophagidae are provided to include the new genus and three newly recorded species discovered after the last work (Kurahashi & Chaiwong, 2013). General morphology, terminology and definition are provided for keys and redescription.

Flies of the genus Hypopygiopsis are forensically important, as their larvae are found to associate with human corpses. In this study, the ultrastructure of larvae and puparia of Hypopygiopsis tumrasvini Kurahashi is presented using scanning electron microscopy (SEM). The larvae are vermiform-shaped, creamy white, and have a smooth integument. The pseudocephalon of larvae bears sensory structures, i.e., antenna, maxillary palpus, and ventral organ. Two tufts of fresh outgrowths (or cerri) were observed along the dorsal margin of the mouth opening of the first instar; whereas a strong mouth hook was apparent in the second and third instars. Keilin's organ, the sensory structure, was noticeable on the ventral surface of the thoracic segments in all instars. In the second and third instars, six conspicuous tubercles were present along the peripheral rims of the last abdominal segment. The puparia were relatively large, measuring 7.77-9.51 mm in length and 3.10-3.97 mm in width. At the latero-dorsal edge of the first abdominal segment, a cluster of ~125 bubble membranes was seen in young puparia; whereas a minute pupal respiratory horn was observed in old one. An SEM image revealed antler-like projections lined within a chamber of a broken pupal respiratory horn. Comparison on number of the bubble membranes of the other blow fly species was shown and the role of pupal respiratory horn compared with other dipterans was discussed.

Flesh flies (Sarcophagidae) are necrophagous insects initially colonizing on a corpse. The species-specific developmental data of the flies collected from a death scene can be used to estimate the minimum postmortem interval (PMImin). Thus, the first crucial step is to correctly identify the fly species. Because of the high similarity among species of flesh flies, DNA-based identification is considered more favorable than morphology-based identification. In this study, we demonstrated the effectiveness of combined sequences (2216 to 2218 bp) of cytochrome c oxidase subunit I and II genes (COI and COII) for identification of the following 14 forensically important flesh fly species in Thailand: Boettcherisca nathani Lopes, Fengia ostindicae (Senior-White), Harpagophalla kempi (Senior-White), Liopygia ruficornis (Fabricius), Lioproctia pattoni (Senior-White), Lioproctia saprianovae (Pape & Bänziger), Parasarcophaga albiceps (Meigen), Parasarcophaga brevicornis (Ho), Parasarcophaga dux (Thomson), Parasarcophaga misera (Walker), Sarcorohdendorfia antilope (Böttcher), Sarcorohdendorfia inextricata (Walker), Sarcorohdendorfia seniorwhitei (Ho) and Seniorwhitea princeps (Wiedemann). Nucleotide variations of Thai flesh flies were evenly distributed throughout the COI-COII genes. Mean intra- and interspecific variations ranged from 0.00 to 0.96% and 5.22% to 12.31%, respectively. Using Best Match (BM) and Best Close Match (BCM) criteria, identification success for the combined genes was 100%, while the All Species Barcodes (ASB) criterion showed 76.74% success. Maximum Likelihood (ML) and Bayesian Inference (BI) phylogenetic analyses yielded similar tree topologies of monophyletic clades between species with very strong support values. The achieved sequences covering 14 forensically important flesh fly species including newly submitted sequences for B. nathani, F. ostindicae and S. seniorwhitei, can serve as a reliable reference database for further forensic entomological research in Thailand and in other areas where those species occur.

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.