The role of parasitoids in suppressing diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), populations was studied for two years (February 2000 - January 2002) on unsprayed cabbage plots near Brits, North West Province, South Africa. Cabbage seedlings were transplanted three consecutive times each year. Infestations by P. xylostella, and the incidence of its parasitoids, were monitored at weekly intervals throughout the study period. The flight activity of P. xylostella male moths was also monitored at weekly intervals using synthetic sex-pheromone traps. Trap catches indicated that moths were active throughout the year and their flight activity corresponded with larval infestations on the crop. Trap catches and infestation levels were low in summer, autumn and winter (December-August) and high in spring (September-November). Eight indigenous parasitic Hymenoptera were reared from P. xylostella: the larval parasitoids Cotesia plutellae (Kurdjumov) (Braconidae) and Apanteles halfordi (Ullyett) (Braconidae), the larval-pupal parasitoids Oomyzus sokolowskii (Kurdjumov) (Eulophidae) and Diadegma mollipla (Holmgren) (Ichneumonidae), the pupal parasitoid Diadromus collaris (Gravenhorst) (Ichneumonidae), and the hyperparasitoids Eurytoma sp. (Eurytomidae), Mesochorus sp. (Ichneumonidae), and Pteromalus sp. (Pteromalidae). Parasitism rates of P xylostella larvae were high reaching 100% on several occasions during late spring, summer and autumn (November-May) each year. Parasitism was lower (50%) in winter and early spring (June-September). Cotesia plutellae was the most abundant parasitoid of P xylostella followed by O. sokolowskii. Both parasitoids were active throughout the year. Apanteles halfordi was absent only in winter. Only one specimen of D. mollipla was recorded, in spring, during this study. A high rate of parasitism of P. xylostella pupae by D. collaris was observed only in spring (September-October). Hyperparasitism rates were high in spring and summer (September-February) when up to 35% of collected R xylostella larvae and C. plutellae cocoons yielded hyperparasitoids. The roles of biotic and abiotic mortality factors on the population dynamics of P. xylostella are discussed. Plutella xylostella (Plutellidae) : Host Apanteles halfordi (Braconidae) : Parasite Cotesia plutellae (Braconidae) : Parasite Diadegma mollipla (Ichneumonidae) : Parasite Diadromus collaris (Ichneumonidae) : Parasite Mesochorus (Ichneumonidae) : Parasite Oomyzus sokolowskii (Eulophidae) : Parasite Eurytoma (Eurytomidae) : Parasite Pteromalus (Pteromalidae) : Parasite Nutrition; Diet; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Habitat; Man made habitat; Land zones; Afrotropical region; Africa Apanteles halfordi; Cotesia plutellae; Diadegma mollipla; Diadromus collaris; Eurytoma; Mesochorus; Oomyzus sokolowskii; Pteromalus; Lepidopteran hosts; Prevalence; unsprayed host food plant crops; Plutella xylostella; Cultivated land habitat; Unsprayed cabbage crops; South Africa; North West Province, Brits region Plutella xylostella; Food plants; Seasonal hymenopteran parasitoid & hyperparasitoid prevalence; unsprayed crops; Brassica oleracea var. capitata (cabbage); Hymenopteran parasites; Population dynamics; Hymenopteran parasitoid & hyperparasitoid prevalence relationship; Seasonal flight activity; Mortality; South Africa; North West Province, Brits region none