none Arthropoda; AVES-; INSECT-PREY; Pieris brassicae (Lepidoptera); Predator role in prey egg & larval mortality Pieris brassicae; HYMENOPTERAN-PARASITES; Apanteles glomeratus; Parasite role in egg & larval mortality; BACTERIAL-DISEASES; Egg & larval mortality; MORTALITY-; Eggs & larvae, roles of predators, parasites & diseases; PREDATORS-; Arthropoda; AVIAN-PREDATORS; Predation role in egg & larval mortality Apanteles glomeratus; LEPIDOPTERAN-HOSTS; Pieris brassicae; Parasite role in host egg & larval mortality The natural causes of mortality in the immature stages of P. brassicae were studied. The aim was to quantify the importance of predators, parasitoids and diseases. Predators were, by the use of exclusion methods, separated into arthropods and vertebrates. The study showed that if the larvae are exposed to predation from both arthropods and vertebrates the total mortality during the larval stages due to predation is 96.9%. If vertebral predation is prevented the survival rates are markedly increased -11 times as many larvae survived to pre-pupae when access from birds was prevented. 81.9% of the prepupae were parasitized by Apanteles glomeratus (L.) (= Cotesia glomerata) (Hym., Braconidae), and 4.0% died from bacterial infections.