Parasitoid dynamics across decomposition stages in cadaver decomposition systems

Parasitoid Hymenoptera associated with necrophagous Diptera represent a potentially valuable but underexplored component of decomposition systems and forensic entomology. This study investigated parasitoid species associated with pupae of Chrysomya megacephala (Fabricius, 1794) exposed during pig cadaver decomposition in the Pampa biome of southern Brazil, and evaluated parasitoid occurrence across decomposition stages and sampling periods. Experiments were conducted in March, September, and November 2024, and January 2025 using 12 pig cadavers. Sentinel pupae were exposed daily throughout decomposition and recovered for parasitoid emergence and identification. Generalized linear mixed models were used to evaluate parasitoidism probability and species-specific occurrence across decomposition stages, while Weibull survival models were applied to analyze stage duration. A total of 5,280 pupae were exposed, of which 376 (7.12%) were parasitized, yielding 4,171 parasitoid adults. Four species were recorded: Nasonia vitripennis (Walker, 1836) (Hymenoptera: Pteromalidae), Pachycrepoideus vindemmiae (Rondani 1875) (Hymenoptera: Pteromalidae), Spalangia endius Walker, 1839 (Hymenoptera: Spalangiidae), and Tachinaephagus zealandicus Ashmead, 1904 (Hymenoptera: Encyrtidae). Parasitoidism probability was significantly lower during the fresh stage and increased from the bloated stage onward. Nasonia vitripennis showed greater contribution during the bloated stage, whereas P. vindemmiae was proportionally more frequent during the fresh stage. Decomposition progressed more rapidly during warmer months, particularly in November and January. Seasonal variation in parasitoidism was also observed, with higher rates during warmer sampling periods. These findings demonstrate that parasitoid assemblages vary across decomposition stages and environmental conditions, highlighting their ecological relevance in decomposition systems and their potential contribution to forensic entomology in subtropical environments.