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In general, the majority of ectoparasitoids of Lepidoptera parasitize larval and/or prepupal stages of the host and do not use the pupal stage, suggesting the presence of ecological and physiological constraints in the evolution of host range. Here, the evidence is given that Agrothereutes lanceolatus, a solitary ectoparasitoid wasp, can exceptionally parasitize host pupae, succeeding to extend its host range to pupal hosts that have a hardened cuticle. Laboratory experiments confirmed that A. lanceolatus developed successfully to adult both on host prepupae and on young pupae in equal proportions. Development time and size of the resulting wasps did not differ between the host types. However, the percentages of hosts producing wasp offspring differed among age classes within the pupal stage. The offspring survival was high except the oldest class of host pupae. With increasing host pupal ages, the offspring size decreased whereas the development time increased. Older host pupae hence were less suitable for the development of offspring. The offspring mortality mostly occurred during the 1st larval stadium without signs of growth, suggesting a difficulty in feeding on host pupae from an external position. Thus, A. lanceolatus can use a wider range of hosts than expected from its ectoparasitic development. The fact may enable A. lanceolatus to be a common and widespread polyphagous species among ectoparasitic Cryptinae.