none Dendrocerus carpenteri (Curtis) was reared in the laboratory on prepupae of Aphidius ervi Haliday (Hymenoptera: Braconidae, Aphidiinae) developing in pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). To test alternative hypotheses about host-marking behaviour and discrimination, we transferred unparasitized and previously parasitized A. ervi prepupae from donor to recipient mummies, which were either "unparasitized" or "parasitized." Females accepted already parasitized hosts within unparasitized mummies, but they rejected unparasitized hosts within previously parasitized mummies. Host discrimination was not influenced by self and conspecific parasitism. Eggs were frequently placed directly on the mummy shell, rather than on the primary parasitoid, or on dummies made from dental wax. Prepupae removed from their mummy shell were not accepted for oviposition. We propose that the "search template" of D. carpenteri is defined, primarily, by the aphid mummy, which is being marked with a contact pheromone after oviposition. Reproduction; Reproductive behaviour; Behaviour; Communication; Chemical signals; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Aphidius ervi (Aphidiidae); Hymenopteran parasites; Dendrocerus carpenteri; Host marking & discrimination behaviour, tests of hypotheses; Hemipteran hosts; Acyrthosiphon pisum; Hymenopteran hyperparasite host marking & discrimination; Evidence for marking of hemipteran host mummies Dendrocerus carpenteri (Ceraphronidae); Egg laying; Discrimination & acceptance of hymenopteran hosts in hemipteran mummies; Pheromones; Marking of hemipteran mummies of hymenopteran primary hosts; Experimental evidence; Hymenopteran hosts; Aphidius ervi; Host discrimination & acceptance; Hyperparasitism; Hymenopteran host discrimination & acceptance; Evidence for oviposition marking of hemipteran secondary host mummies Acyrthosiphon pisum (Aphidoidea); Hymenopteran parasites; Aphidius ervi & Dendrocerus carpenteri; Host marking & discrimination by hyperparasite, experimental study