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

Abstract

The phenology of native brachycerine weevil species at seven pasture sites in Otago, Canterbury and Waikato was studied by regular quantitative sampling of adults. Weevils were identified to species, and dissected to record reproductive status and parasitism by introduced braconid parasitoids in the genus Microctonus. Climatic data assisted in the interpretation of some population density patterns. Weevil population density was estimated for periods of two to five years at the selected sites. Species in the Entimini (species of Irenimus and Nicaeana) were generally univoltine, with adults Z99025 emerging in winter-spring. The main period of reproductive activity was spring, and parasitism by Microctonus aethiopoides reached its highest incidence in 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 in Otago, parasitism by M. aethiopoides was higher and could have affected the population density of Irenimus aemulator (Broun) and Nicaeana sp. Most parasitism 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, differed from the entimines because adults emerged in autumn and spring, and may be bivoltine. Mechanisms of M. aethiopoides parasitism of non-target species in the field are discussed.

Host specificity testing and suitability of a European biotype of the braconid parasitoidMicroctonus aethiopoidesas a biological control agent againstSitona lepidus(Coleoptera: Curculionidae) in New Zealand

“…Given the abundance of the host plant of S. lepidus , white clover (T. repens ), throughout New Zealand, there is no reason to suspect that European M. aethiopoides ' impact on non-target species would be in any way avoided through geographical separation. Nonetheless, despite the high levels of parasitism shown by the Moroccan M. aethiopoides in laboratory tests, several years of postrelease field monitoring has indicated that parasitism of endemic weevils inhabiting indigenous grasslands have never exceeded 10% (unpublished data), although higher levels than this have been found in weevils living in developed pasture at lower altitudes (Barratt et al 1997b(Barratt et al , 2000.…”

“…In the field, the parasitoid has parasitised 13 New Zealand and four exotic species from five tribes and two subfamilies of Curculionidae (Barratt et al 2000;Barratt 2004). Such a wide host range has contributed to increased concern in New Zealand about the impacts of biological control agents on non-target species (e.g., Barratt et al 1999b).…”

Methods Used to Assess Non-target Effects of Invertebrate Biological Control Agents of Arthropod Pests

“…First, one or several nontarget species were selected and sampled in areas where the biological control agent was released or was known to occur (e.g. Barratt et al, 2000). Such sampling makes it possible to compare the host range found in the laboratory with field host range.…”

Potential exposure of a classical biological control agent of the soybean aphid, Aphis glycines, on non-target aphids in North America

“…Additionally, a number of studies in both weed and arthropod biological control have shown that geographic and temporal differences in overlap between biological control agents and nontarget species can greatly influence the overall risk to non-targets (e.g. Barratt et al 2000;Pemberton 2000;Follett et al 2000).…”