none Parasitoids of concealed hosts have to drill through a substrate with their ovipositor for successful parasitization. Hymenopteran species in this drill-and-sting guild locate immobile pupal hosts by vibrational sounding, i.e., echolocation on solid substrate. Although this host location strategy is assumed to be common among the Orussidae and Ichneumonidae there is no information yet whether it is adapted to characteristics of the host microhabitat. This study examined the effect of substrate density on responsiveness and host location efficiency in two pupal parasitoids, Pimpla turionellae and Xanthopimpla stemmator (Hymenoptera: Ichneumonidae), with different host-niche specialization and corresponding ovipositor morphology. Location and frequency of ovipositor insertions were scored on cylindrical plant stem models of various densities. Substrate density had a significant negative effect on responsiveness, number of ovipositor insertions, and host location precision in both species. The more niche-specific species X. stemmator showed a higher host location precision and insertion activity. We could show that vibrational sounding is obviously adapted to the host microhabitat of the parasitoid species using this host location strategy. We suggest the attenuation of pulses during vibrational sounding as the energetically costly limiting factor for this adaptation. Sensory reception; Sound reception; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Galleria mellonella (Pyralidae); Hymenopteran parasites; Pimpla & Xanthopimpla; Host location, vibrational sounding efficiency in relation to substrate density Pimpla turionellae; Xanthopimpla stemmator (Ichneumonidae ); Echolocation; Vibrational sounding; Lepidopteran hosts; Galleria mellonella; Host location, vibrational sounding efficiency in relation to substrate density