none Nutrition; Diet; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Population dynamics; Habitat; Man made habitat; Land and freshwater zones; Palaearctic region; Europe Psila rosae (Psilidae); Food plants; Daucus carota (carrot), effect of parasite & plantation habitat; Hymenopteran parasites; Dacnusa gracilis; Prevalence & host density relationship; Prevalence; Dacnusa gracilis (Hymenoptera) parasite; Population density; Plantation habitat & hymenopteran parasite effects; Cultivated land habitat; Plantation conditions effect on density on food plant; Poland; Population density on food plant, effects of habitat & parasite Acrolepia assectella (Yponomeutidae); Food plants; Allium porrum (leek), effect of parasite & plantation habitat; Hymenopteran parasites; Braconidae & Ichneumonidae; Prevalence & host density relationship; Prevalence; Braconidae & Ichneumonidae (Hymenoptera) parasites; Population density; Plantation habitat & hymenopteran parasite effects; Cultivated land habitat; Plantation conditions effect on density on food plant; Poland; Population density on food plant, effects of habitat & parasite Hymenoptera; Prevalence; Acrolepia (Lepidoptera) & Psila (Diptera) hosts; Poland; Prevalence & dipteran & lepidopteran host density relationships Braconidae; Ichneumonidae; Lepidopteran hosts; Acrolepia assectella; Prevalence & host density relationship; Poland Dacnusa gracilis (Braconidae); Dipteran hosts; Psila rosae; Prevalence & host density relationship; Poland