noneEnter Population fluctuation and percentages of parasitism were determined for Copitarsia decolora (Guenee), Plutella xylostella L. and Trichoplusia ni Hubner on three varieties of B. oleracea, cabbage, cauliflower and broccoli, from April 2004 trough April 2005, in Acatzingo, Puebla, Mexico. Every 14 days randomized samplings in 10 plants by crop were made; the total number of larvae were recorded, collected and maintained in a rearing room at 27[degree] C [plus or minus] 1[degree] C and 75% [plus or minus] 5% of relative humidity for parasitoid development. The pest population was more abundant during head formation in cabbage and pellet formation in broccoli and cauliflower. The greatest density was observed in cabbage, with values of 1.3, 12.3 and 2.4 larvae by plant, for C. decolora, P. xylostella and T. ni, respectively. Diadegma insulare Cresson (Hymenoptera: Ichneumonidae) was obtained from P. xylostella larvae, whereas Voria ruralis Fallen (Diptera: Tachinidae) was obt! ained from T. ni larvae. The mean rate of parasitism for D. insulare was 46.78% and for V. ruralis only 0.7%. The population density and rates of parasitism were negatively affected by insecticide application on the crops of broccoli, cabbage and cauliflower. BR Nutrition. Diet. Parasites diseases and disorders. Parasites. Insect parasites. Hosts. Insect hosts. Ecology. Population dynamics. Land zones. Nearctic region. North America. Voria ruralis (Tachinidae): Parasite; Diadegma insulare (Ichneumonidae): Parasite; Copitarsia decolora (Noctuidae); Trichoplusia ni (Noctuidae): Host; Plutella xylostella (Plutellidae): Host. Copitarsia decolora: Food plants, Brassica oleracea, Population density, pest status, larva, Mexico, Puebla, Acatzingo; Diadegma insulare: Lepidopteran hosts, Plutella xylostella, Mexico, Puebla, Acatzingo, prevalence; Plutella xylostella: Food plants, Brassica oleracea, Hymenopteran parasites, Diadegma insulare, Population density, pest status, larva, Mexico, Puebla, Acatzingo; Trichoplusia ni: Food plants, Brassica oleracea, Dipteran parasites, Voria ruralis, Population density, pest status, larva, Mexico, Puebla, Acatzingo; Voria ruralis: Lepidopteran hosts, Trichoplusia ni, Mexico, Puebla, Acatzingo, prevalence. ST Animalia, Arthropoda, Insecta, Diptera, Brachycera, Cyclorrhapha, Tachinidae; Animalia, Arthropoda, Insecta, Hymenoptera, Apocrita, Terebrantia, Ichneumonoidea, Ichneumonidae; Animalia, Arthropoda, Insecta, Lepidoptera, Glossata, Heteroneura, Noctuoidea, Noctuidae; Animalia, Arthropoda, Insecta, Lepidoptera, Glossata, Heteroneura, Yponomeutoidea, Plutellidae. Arthropods; Hymenopterans; Insects; Invertebrates; Lepidopterans; True Flies.