Host specificity testing and suitability of a European biotype of the braconid parasitoid Microctonus aethiopoides as a biological control agent against Sitona lepidus (Coleoptera: Curculionidae) in New Zealand

The European biotype of the parasitoid Microctonus aethiopoides Loan ( Hymenoptera: Braconidae) is being considered for release against Sitona lepidus Gyllenhal ( Coleoptera: Curculionidae) in New Zealand. Host specificity was evaluated in the laboratory using both endemic and introduced weed biological control curculionid species, with 12 no-choice and three choice experiments carried out comparing the S. lepidus and test weevils. Two further no-choice tests used the Moroccan M. aethiopoides biotype to compare attack rate between European and Moroccan M. aethiopoides, the latter released in 1982 to control the lucerne pest S. discoideus. Across all experiments, total parasitism of S. lepidus was 69% compared with 15% for the test weevils. European M. aethiopoides was able to develop in the native weevils Irenimus aequalis, Nicaeana cervina, Catoptes cuspidatus, Protolobus porculus and Steriphus variabilis with parasitism rates of 13, 28, 2, 7 and 8%, respectively. These levels were significantly less than those in the corresponding S. lepidus control. Total parasitism of I. aequalis and C. cuspidatus increased significantly in the presence of S. lepidus than recorded under no-choice conditions. The presence of European M. aethiopoides caused minor, if any, test weevil mortality prior to the onset of prepupal emergence and there was no significant reproductive suppression in parasitoid-exposed test weevils. Parasitism of the introduced weed control agent R. conicus by European M. aethiopoides was significantly lower (1.1%) compared to the Moroccan biotype (47.5%). Based on these and other experiments, should the European M. aethiopoides be released as a biological control agent of S. lepidus, its ecological impacts are likely to be less severe than those already exhibited by the Moroccan M. aethiopoides.