Phenology of native weevils (Coleoptera : Curculionidae) in New Zealand pastures and parasitism by the introduced braconid, Microctonus aethiopoides Loan (Hymenoptera : Braconidae)

The phenology of native brachycerine weevil species at seven pasture sites in Otago, Canterbury and Waikato was studied by regular quantitative sampli ng of adults. Weevils were identified to species, and dissected to record r eproductive status and parasitism by introduced braconid parasitoids in the genus Microctonus. Climatic data assisted in the interpretation of some po pulation density patterns. Weevil population density was estimated for peri ods of two to five years at the selected sites. Species in the Entimini (sp ecies of Irenimus and Nicaeana) were generally univoltine, with adults emer ging in winter-spring. The main period of reproductive activity was spring, and parasitism by Microctonus aethiopoides reached its highest incidence i n January. Low level parasitism of native weevil species by M. aethiopoides was detected at all sites, and by M. hyperodae at two sites. At one site i n Otago, parasitism by M. aethiopoides was higher and could have affected t he population density of Irenimus aemulator (Broun) and Nicaeana sp. Most p arasitism occurred after the main reproductive period of weevils in spring, but a putative second generation in some species might be more affected by parasitoid attack. A native rhytirhinine species, Steriphus variabilis, di ffered from the entimines because adults emerged in autumn and spring, and may be bivoltine. Mechanisms of M. aethiopoides parasitism of non-target sp ecies in the field are discussed.