Host pupae as an ecological resource for parasitoid Hymenoptera associated with Diptera

Dipteran pupae represent a distinctive ecological resource for parasitoid Hymenoptera because they are immobile, developmentally defined, and frequently concentrated in concealed microhabitats where they remain available for host exploitation. This integrative descriptive review examined the biological sequence through which fly pupae and puparia are located, evaluated, parasitized, and converted into parasitoid offspring. The synthesis emphasized pupation site, host accessibility, concealment, burial depth, host recognition, oviposition, ectoparasitic and endoparasitic development, idiobiont and koinobiont strategies, solitary and gregarious development, host mortality, and adult emergence. Confirmed host–parasitoid relationships were retained when supported by direct emergence or equivalent evidence linking the parasitoid to a defined dipteran host. The results showed that pupae may occur in exposed substrates, soil, sand, manure, decomposing organic material, and other protected microsites, creating substantial variation in parasitoid access. Host suitability was further influenced by developmental stage, size, physiological condition, and the physical properties of the puparium. Solitary and gregarious strategies produced different relationships between host mortality and parasitoid abundance, demonstrating that the number of emerging parasitoids cannot be equated directly with the number of parasitized hosts. Burial, concealment, substrate structure, and pupation depth acted as ecological filters that could reduce host discovery even when the pupa was physiologically suitable. The evidence supports a resource-centered interpretation in which the dipteran pupa is viewed not merely as a developmental stage, but as a spatially and physiologically structured resource whose accessibility and quality determine parasitoid success. This framework integrates host location, acceptance, parasitism, development, mortality, and emergence without requiring inferential statistical comparison. By organizing these processes around the host rather than the parasitoid taxon, the review provides a biological framework for interpreting variation in pupal exploitation across substrates, environments, and developmental contexts