Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 for biological control of Sitona discoideus Gyllenhal in lucerne. Parasitism of Rhinocyllus conicus Froelich (Coleoptera: Curculionidae) by M. aethiopoides was first recorded in 1994. By 1997 parasitised R. conicus had been detected in seven lucerne stands, with up to 16% of weevils parasitised. This study investigated if parasitism of R. conicus by M. aethiopoides occurred only within lucerne. In December 1998 adult R. conicus were collected from nodding thistles in lucerne stands and in pasture at eight sites, in the Hakataramea and Waitaki Valleys, South Canterbury, and in the Strath Taieri, Otago and held in cages for four weeks. Parasitoids emerged from weevils from seven lucerne stands (range 0-12% (mean 4.4, SEM 1.44)) and seven pastures (0-29% (mean 6.5, SEM 3.3)). The difference between habitats was not significant (SED 3.98). There was no relationship between R. conicus density and the proportion of weevils parasitised within either habitat and neither was the proportion of weevils parasitised in a habitat related to the proportion parasitised in the other habitat. Parasitism of R. conicus by M. aethiopoides appears to be more common than previously thought but the significance of this parasitism within both lucerne and pasture is still to be determined.

Previous studies have suggested that the braconid parasitoid Microctonus aethiopoides Loan oviposits in its target host Sitona discoideus (Kuschel) primarily during light periods, and therefore, diurnally active non-target weevils may be more susceptible to parasitism than nocturnally active weevils. A laboratory investigation was carried out to measure the circadian feeding and oviposition activity patterns of three known non-target hosts of M. aethiopoides. M. aethiopoides was also exposed to Listronotus bonariensis Gyllenhal, a crepuscularly active weevil, in light or dark periods or continuously over a 16 hour light: 8 hour dark photoperiod. Feeding by two native species increased during the light period, while that of the introduced Rhinocyllus conicus (Froelich) remained relatively constant throughout the light-dark cycle. Neither of the native species showed a consistent circadian oviposition pattern. R. conicus laid more eggs during light than dark periods. M. aethiopoides oviposited in L. bonariensis equally during light and dark periods.