A population of the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) (DBM) was recently found to infest sugar snap- and snowpeas in the Rift Valley in Kenya, causing heavy damage. The influence of this host shift on host location preferences of two parasitoids was investigated: The indigenous Diadegma mollipla (Holmgren) regarded as a relative generalist, and Diadegma semiclausum (Hellen), regarded as highly specific to DBM. The attractiveness of different odour sources was compared for the two parasitoid species using a Y-tube olfactometer using naive females. D. mollipla was not significantly attracted to any cabbage related odours but showed a significant preference for the DBM infested pea plant when tested against clean air. D. semiclausum was highly attracted to the undamaged cabbage plant and odours related to cabbage. On the other hand, peas infested with DBM, showed no attractiveness to this parasitoid. The results showed that specialisation of D. semiclausum is mediated by host plant signals, associated with crucifers, which are not encountered in DBM feeding on peas. For D. mollipla,although a frequent parasitoid on DBM in crucifers, volatiles emitted by these plants might not be used as primary cues for host location. This species may respond largely to chemicals yet unknown and associated with a variety of plant-herbivore interactions. Plutella xylostella (Plutellidae) : Host Diadegma mollipla (Ichneumonidae) : Parasite Diadegma semiclausum (Ichneumonidae) : Parasite Nutrition; Diet; Behaviour; Orientation; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Afrotropical region; Africa Diadegma mollipla; Diadegma semiclausum; Taxis; Chemotaxis; Lepidopteran hosts; Chemotactic response to host food plant shift; Plutella xylostella; Kenya; Maragua & Wundanyi Plutella xylostella; Food plants; Cabbage, pea & potato; Hymenopteran parasites; Parasites chemotactic response to food plant shift; Diadegma; Kenya; Maragua & Wundanyi none