Non-target parasitism of endemic weevils by introduced Microctonus (Hymenoptera: Braconidae) species in tussock grasslands of Otago and Southland, New Zealand

Abstract

The parasitoids Microctonus aethiopoides Loan (Moroccan and Irish ecotypes) and M. hyperodae Loan (Hymenoptera: Braconidae) have been introduced to New Zealand as biological control agents for agricultural pest weevils Sitona discoideus Gyllenhal, S. obsoletus Gmelin and Listronotus bonariensis (Kuschel). These parasitoids are also present in native tussock grassland habitats and a survey carried out over two years at nine tussock grassland sites demonstrated that several endemic weevil species were parasitized by these biological control agents within these habitats. New records of non-target parasitism were found for the endemic species of Chalepistes, Nicaeana, and Eugnomus. It was found that M. aethiopoides is established and cycling within weevil communities in these environments, using endemic weevil hosts in part, but pathways also exist via three pest weevil species for spillover from agricultural environments. Parasitism of endemic weevils was not found to be ubiquitous in these environments and parasitism levels were mostly below 10%.