none Effects of insecticide resistance of Plutella xylostella on parasitism capacity of Cotesia plutellae were studied in the presence of fenvalerate under laboratory conditions. In the condition where the insecticide was applied, parasitism of a resistant strain (RRP) of P. xylostella by a strain (RRC) of C. plutellae reared from the resistant host strain reached 89 % and survival of the exposed host larvae reached 95 %, significantly higher than when RRC was provided with host larvae of a susceptible strain (SSP) of P. xylostellae or when a strain (SSC) of C. plutellae reared from SSP was provided with SSP larvae. These results indicated that resistant host larvae survived better the insecticide application than susceptible ones and thus provided more hosts for the parasitoid in favour of the population increase of the latter. Statistical analysis by ANOVA showed that host strains and the interactions between strains of P. xylostella and C. plutellae had significant effects on parasitism and death rate of P. xylostella larvae, indicating that insecticide resistance of P. xylostella had changed its suitability to C. plutellae. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Abiotic factors; Chemical factors Plutella xylostella (Plutellidae); Hymenopteran parasites; Cotesia plutellae; Survival & prevalence, insecticide resistance effects; Survival; Fertilizers and pesticides; Fenvalerate Cotesia plutellae (Braconidae); Lepidopteran hosts; Plutella xylostella; Prevalence & effect on host survival, host insecticide resistance relations