noneEnter The diamondback moth, Plutella xylostella (L.) is considered a specialist on Brassicaceae, but it is capable of expanding its food range by incorporation of non-brassicaceous plants into its diet. The use of a new food plant may change food availability and vulnerability of P. xylostella to its natural enemies, especially specialist parasitoids. In this laboratory study, we evaluated the bottom-up effects of two Brassicaceae viz. Brassica napus L. and Descurainia sophia (L.) Webb ex Prantl and two non-Brassicaceae viz. Tropaeolum majus L. and Cleoine hassleriana Chodat on several fitness correlates of the specialist parasitoid, Diadegma insulare (Cresson) reared on P. xylostella larvae. Percentage of parasitism of host larvae by D. insulare varied among the plant species and was highest on T majus and lowest on D. sophia. Values of several fitness correlates for D. insulare differed when the host was feeding on various plant species. Egg to adult development was fastest on B. napus followed by C. hassleriana, D. sophia and T majus. Female wasps reared on C hasseleriana lived the longest in absence of food. The response of D. insulare to potential food-plant expansion by its host P. xylostella is discussed. [copyright]2009 Gesellschaft fur Okologie. Published by Elsevier GrnbH. All rights reserved. BR Nutrition. Diet. Life cycle and development. Evolution. Parasites diseases and disorders. Parasites. Insect parasites. Hosts. Insect hosts. Ecology. Diadegma insulare (Ichneumonidae): Parasite; Plutella xylostella (Plutellidae): Host. Diadegma insulare: Development, Developmental rate, host parasite relationships, host plant choice effects, female, male, Natural selection, Fitness levels, Lepidopteran hosts, Plutella xylostella, Trophic structure, Tritrophic interactions; Plutella xylostella: Food plants, Brassiaceous and non-brassiaceous plants, host plant choice effects on parasitoid fitness, larva, Hymenopteran parasites, Diadegma insulare, Trophic structure, Tritrophic interactions. ST Animalia, Arthropoda, Insecta, Hymenoptera, Apocrita, Terebrantia, Ichneumonoidea, Ichneumonidae; Animalia, Arthropoda, Insecta, Lepidoptera, Glossata, Heteroneura, Yponomeutoidea, Plutellidae. Arthropods; Hymenopterans; Insects; Invertebrates; Lepidopterans.