Forensic entomology offers unique advantages for the minimum postmortem interval (PMImin) estimation of decomposed corpses in forensic investigations. Accurate species identification and up-to-date locality information are essential. Hainan Island has a tropical rainforest climate and a vast territory. In this study, the community structure of necrophagous flies on Hainan Island was investigated in detail according to geographical environment. The results showed that the dominant species included C. megacephala, S. peregrina, C. rufifacies, S. misera, H. ligurriens, S. sericea, S. cinerea, S. dux, C. pinguis, and M. domestica. Furthermore, C. rufifacies and C. villeneuvi were found only in the high-altitude areas of Wuzhi Mountain, while S. cinerea was distributed only in coastal areas; the latter is a representative species of Hainan Island and has not been reported before. Furthermore, a GenBank database of forensically important flies was established, whilst a high-resolution melt (HRM) curve analysis was applied to identify the common species of Hainan Island for the first time. This study enriches the database of forensically important flies in tropical rainforest regions.

Molecular species identification plays an increasingly important role in forensic entomology and is centered on selecting appropriate DNA barcodes, which there are not yet enough of. Such identification is decisive in discovering a better DNA barcode for the identification of necrophilous fly species. Here, we analyzed 10 common necrophilous fly species found on Hainan Island; designed 12 pairs of fly-specific primers from different mitochondrial regions; screened two fly DNA barcodes with better results than those of published studies, which were used as controls; and employed a high-resolution melting (HRM) curve to construct PCR-HRM technology systems for rapid and efficient necrophilous fly species identification. The results showed that, among the 14 DNA barcoding PCR-HRM systems, the newly designed COXII-519/COXII-615 primer was the best, which identified 10 necrophilous fly species in one test. The second-best system was the C1-J-2495/C1-N-2800 primer published in the literature, which identified six fly species in one test. Moreover, since the COXII-519/COXII-615 primer system performed successfully in both stale (stored over two years) and larval samples due to its short amplificated fragment (shorter than 97 bp), it may serve as a new efficient DNA barcode for necrophilic fly species identification. The new DNA barcoding PCR-HRM system established in this study enables the rapid and accurate identification of necrophilic fly species.

Morphological classification is the gold standard for identifying necrophilous flies, but its complexity and the scarcity of experts make accurate classification challenging. The development of artificial intelligence for autonomous recognition holds promise as a new approach to improve the efficiency and accuracy of fly morphology identification. In our previous study, we developed a GLB-ViT (Global–Local Balanced Vision Transformer)-based deep learning model for fly species identification, which demonstrated improved identification capabilities. To expand the model’s application scope to meet the practical needs of forensic science, we extended the model based on the forensic science practice scenarios, increased the database of identifiable sarcosaphagous fly species, and successfully developed a WeChat Mini Program based on the model. The results show that the model can achieve fast and effective identification of ten common sarcosaphagous flies in Hainan, and the overall correct rate reaches 94.00%. For the few cases of identification difficulties and suspicious results, we have also constructed a rapid molecular species identification system based on DNA Barcoding technology to achieve accurate species identification of the flies under study. As the local fly database continues to be improved, the model is expected to be applicable to local forensic practice.

Carcass decomposition and necrophagous fly activity provide important forensic evidence for postmortem interval estimation, yet data from tropical island environments remain limited. This study investigated decomposition characteristics, the relationship between total body score (TBS) and accumulated degree days (ADD), and changes in necrophagous fly communities on Hainan Island. In May 2025, 10 pig carcasses were placed simultaneously at five sites. Decomposition was recorded continuously using a pig-specific TBS system, environmental temperature and relative humidity were monitored, and adult flies were collected with Malaise traps and identified morphologically. All carcasses passed through the fresh, bloated, active decay, advanced decay, and skeletonization stages. Decomposition proceeded rapidly overall, although some variation occurred among regions and individuals. TBS showed a strong relationship with accumulated thermal input, and the log10(ADD) model provided a better fit than the raw ADD model. A total of 15,054 necrophagous flies representing 24 species from 13 genera and 5 families were collected. Calliphoridae was the dominant family, and Chrysomya nigripes Aubertin, 1932, was the absolute dominant species. This study provides reference data for forensic entomology under tropical conditions on Hainan Island.

Laterite is an acidic tropical soil enriched in iron and manganese. It is common at tropical death scenes, yet its effect on necrophagous insect development is unstudied. We raised the forensically important blow fly Chrysomya megacephala (Fabricius, 1794) on three Hainan laterites, a yellow earth control, and a no-soil substrate. We combined larval phenotyping, inductively coupled plasma mass spectrometry (ICP-MS), and untargeted ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) metabolomics of whole larvae sampled on Days 1–3 post-burrowing. Laterites were strongly acidic (pH 4.17–4.32 vs. 7.45) and Fe/Mn-enriched. Whole-larval Fe (~10.2-fold) and Mn (~4.1-fold; whole larvae including gut contents, as no gut evacuation was performed) were consistently elevated across the three laterites, without biomagnification (bioaccumulation factors < 1). Laterite-group larvae were significantly heavier from 106 h and shorter from 130 h of age. They entered the cryptocephalic stage at 130 vs. 154 h and pupariated 24 h earlier in shallower soil (3–5 vs. 8–10 cm). In the primary merged metabolome analysis (n = 5–6 per group; 2975 metabolites), no metabolite survived the Benjamini–Hochberg correction in any laterite comparison, whereas three did in the no-soil comparison. The level-1 candidate metabolites are therefore hypothesis-generating. Laterite thus alters larval development and whole-body metal content. This implies a potential ~1-day bias in postmortem interval estimation under controlled conditions.