HOST SPECIFICITY TESTING AND SUITABILITY OF THE PARASITOID MICROCTONUS-HYPERODAE (HYM, BRACONIDAE, EUPHORINAE) AS A BIOLOGICAL-CONTROL AGENT OF LISTRONOTUS-BONARIENSIS (COL, CURCULIONIDAE) IN NEW-ZEALAND

The behaviour of the parasitoid Microctonus hyperodae Loan was studied under quarantine conditions to determine its likely host range in New Zealand. The species was imported from South America as a potential biological control agent of Argentine stem weevil, Listronotus bonariensis (Kuschel). The study involved systematic evaluation of the parasitoid's behaviour when exposed to 24 non-host weevil species ; all but three of these were native to New Zealand. Of those tested, four were found to sustain some M. hyperodae development. However, further examination showed that in all but one species, Irenimus aequalis (Broun), parasitoid development was impeded, with up to 50 % of the larvae becoming encapsulated. Overall, those weevil species that were attacked produced only 19 % of the parasitoids derived from L. bonariensis controls. As an adjunct to this quarantine study, a review of the habitats of the native weevil and target pest populations indicated that refugia would probably exist for native alpine species. I. aequalis was not considered to be threatened by M. hyperodae as this weevil has benefited from the advent of European agricultural systems to the extent that it is now recognised as a minor pest. In view of its relatively oligophagous behaviour, the parasitoid was recommended as suitable for release.