none Sampling of maize fields in South Auckland revealed a mean density of 1.86 M. separata Walker larvae per plant. Seventy-eight percent of 6th and 7th instar larvae were parasitised by the introduced gregarious braconid, A. ruficrus Halliday. Hyper-parasitism by Eupteromalus spp. was widespread but not significant. Spatial distribution of M. separata and A. ruficrus was heterogeneous between and within fields. This is tentatively attributed to aerial concentration of adult moths resulting from climatic factors, and this is judged to be the most likely mechanism for armyworm outbreaks. Populations were shown to be amenable to accurate estimation with relatively few samples. There was no correlation between M. separata population size and weed cover within sample plots. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Population dynamics; Land and freshwater zones; Australasian region Mythimna separata (Noctuidae); Hymenopteran parasites; Apanteles ruficrus, hyperparasitism relationships; Hyperparasitism; Apanteles ruficrus (Hymenoptera) parasites with; Eupteromalus (Hymenoptera) parasites; Prevalence; Apanteles ruficrus (Hymenoptera) parasites, hyperparasitism effects; Population size; Incidence on food plants, hymenopteran parasites relationship; New Zealand; South Auckland; Population size on food plants & hymenopteran parasites prevalence Apanteles ruficrus (Braconidae); Lepidopteran hosts; Mythimna separata; Prevalence, hyperparasitism relationships; Hyperparasitism; Eupteromalus parasites of cocoon masses emerged from; Mythimna separata (Lepidoptera) host; New Zealand; South Auckland; Hyperparasitism interrelationships Eupteromalus (Pteromalidae); Hymenopteran hosts; Apanteles ruficrus; Prevalence, hyperparasitism; New Zealand; South Auckland; Hyperparasitism interrelationships