Learning of host and host-plant recognition in the larval parasitoid Diadegma semiclausum Hellen (Hym., Ichneumonidae) was studied. The results show that the host-plants fed on by host larvae of parasitoids during their immature stages did not affect host-plant preference of the ensuing female adults, but brief experiences by female parasitoids at early adult stages significantly affected their subsequent host preferences. Female parasitoids showed significant preferences for plant volatiles they had previously experienced. However, such preferences acquired through learning could be modified by new experiences. Female parasitoids could learn not only the volatile chemicals emitted by host-infested plants, but also the infochemicals emitted by host larvae. Nutrition; Diet; Behaviour; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Plutella xylostella (Plutellidae); Food plants; Brassica campestris & Brassica oleracea; Hymenopteran parasites; Diadegma semiclausum; Host infested food plant recognition learning by parasite Diadegma semiclausum (Ichneumonidae); Learning; Lepidopteran hosts; Plutella xylostella; Host infested food plant recognition learning none