Cleopus japonicus Wingelmuller (Coleoptera: Curculionidae) is being considered for release to control buddleia Buddleja davidii in New Zealand. As part of the pre-release testing, Moroccan and Irish biotypes of the solitary endoparasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae) were evaluated for potential non-target impacts on adult C. japonicus should release occur. Laboratory experiments evaluated both the behavioural and physiological suitability of C. japonicus to both biotypes of the parasitoid. Parasitoid behavioural attraction was assessed using the pathenogenic Bacterium Serratia marcescens (Enterobactereaceae), as an indicator of ovipositor penetration. Physiological suitability was assessed by comparing parasitism of C. japonicus with the natural hosts of the respective parasitoid biotypes. The parasitoid-bacteria study showed that C. japonicus was behaviourally acceptable to both Moroccan and Irish M. aethiopoides, with the two experiments producing 34% and 8% mortality, respectively. Cleopus japonicus did not support development of either Moroccan or Irish M. aethiopoides biotypes. None of the weevils dissected at the end of the experiment contained immature parasitoids. Comparison between unexposed and parasitoid-exposed C. japonicus found no difference in premature mortality during the experiment nor in the number of fully reproductive females at its conclusion. The results of this study predict that should C. japonicus be released, the potential impact of M. aethiopoides on field populations will be negligible. Cleopus japonicus (Curculionidae) : Host Microctonus aethiopoides (Braconidae) : Parasite Reproduction; Reproductive behaviour; Life cycle and development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Cleopus japonicus; Hymenopteran parasites; Potential non-target impact of parasite strains; experimental study & wider implications; Microctonus aethiopoides Microctonus aethiopoides; Egg laying; Development; Coleopteran hosts; Potential non-target impact of parasite strains; experimental study & wider implications; Cleopus japonicus none