Population densities of the endemic red admiral butterfly, Bassaris gonerilla, were monitored over two summers on Banks Peninsula, New Zealand. Egg-laying usually begins in September and ends in late May. Peaks in egg, larval and adult densities suggest that B. gonerilla completes two full generations per season and in favourable years, a third generation is started but not completed. Population density was lower in a low-rainfall season probably because of the lower survival and nutritional quality of the host plant, Urtica ferox. "Non-target" parasitism levels by Pteromalus puparum (introduced to manage populations of the small white butterfly Pieris rapae) were low at 3.5-16.9% of pupae collected from the field. However, parasitism by the self-introduced pupal parasitoid Echthromorpha intricatoria was very high at 67.5-82.3%. Echthromorpha intricatoria can overwinter in B. gonerilla pupae and is thus capable of attacking all generations of B. gonerilla. More long-term data are needed to determine the status of, and regulatory mechanisms affecting B. gonerilla populations. Life cycle and development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Australasian region; Australasia Bassaris gonerilla (Nymphalidae); Life cycle; Phenology; Hymenopteran parasites; Echthromorpha & Pteromalus; Pupal parasitism levels; New Zealand; Banks Peninsula; Phenology & pupal parasitism levels Echthromorpha intricatoria (Ichneumonidae ); Pteromalus puparum (Pteromalidae ); Lepidopteran hosts; Bassaris gonerilla; New Zealand; Banks Peninsula; Pupal parasitism levels, lepidopteran host none