The basic reproductive biology of two ectoparasitoids developing on the late larval instars of the scolytid Ips typographus Linnaeus, a pest of spruce forests in Eurasia, was studied with the purpose of explaining which biological features allow the two species to share the same host. The anautogenous braconid Coeloides bostrichorum Giraud had a longer pre-oviposition period (5.1 vs. 3.3 days), a greater egg load (8.1 vs. 6.1 eggs), survived longer and emerged later than the pteromalid Rhopalicus tutela (Walker). In contrast, R. tutela was autogenous and tended to be more fecund under constrained conditions (9.7 vs. 5.1 total offspring per female). The longer pre-oviposition period of the specialist C. bostrichorum, coupled with its greater longevity, afforded the opportunity of better synchronization of ovipositing females with late instar larvae of I. typographus. By contrast, the polyphagous R. tutela matured rapidly, allowing parasitism of both younger and older larval instars of I. typographus in addition to other species. These small differences favoured the co-occurrence of the two parasitoid species on the same attacked trees. Reproduction; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Palaearctic region; Eurasia; Europe Ips typographus (Curculionidae); Hymenopteran parasites; Coeloides bostrichorum & Rhopalicus tutela; Parasite reproductive biology related to host preference; Belgium; South; Hymenopteran parasite reproductive biology related to host preference Coeloides bostrichorum (Braconidae ); Rhopalicus tutela (Pteromalidae ); Reproduction; Coleopteran hosts; Ips typographus; Belgium; South, parasite reproductive biology related to host preference none