Incidence of the armyworm,Mythimna separataWalker (Noctuidae:Lepidoptera), and its introduced parasite,Apanteles ruficrusHalliday (Braconidae:Hymenoptera), in maize

Abstract

Sampling of maize fields in South Auckland revealed a mean density of 1.86 Mythimna separata Walker larvae per plant. Seventy-eight percent of 6th and 7th instar larvae were parasitised by the introduced gregarious braconid, Apanteles 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.