Effects of Tropical Laterite Soils on Larval Development and the Metabolome of the Forensically Important Blow Fly Chrysomya megacephala (Diptera: Calliphoridae): An Exploratory Study

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.