S. L. Goldson

Geographical origin of an introduced insect pest, Listronotus bonariensis (Kuschel), determined by RAPD analysis.

The Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae), is an important introduced pasture pest in New Zealand. In this study geographical populations of this species were analysed using polymerase chain reaction-based randomly amplified polymorphic DNA (RAPD), in an attempt to determine the geographical origin of the pest. Morphologically indistinguishable individuals were collected from nine South American, five New Zealand and one Australian populations. Ten primers were screened for usefulness, two of which revealed significant, scorable polymorphisms between these populations. The results indicated that the sampled New Zealand L. bonariensis populations originated from the east coast of South America.

Reproductive diapause in the Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae), in New Zealand.

To improve the precision of understanding of the phenology of Listronotus bonariensis (Kuschel), samples were collected at regular intervals near Canterbury, New Zealand, and the seasonal changes in their reproductive morphology monitored by regular dissection. It was demonstrated that the adult weevils enter hibernatory reproductive diapause in early March and remain in this state until late July when reproductive activity resumes. Adults emerging in February may enter diapause immediately. The existence of diapause was further supported by its associated cessation of mating, increase in body fat and apparent drop in the haemolymph titre of juvenile hormone. Laboratory experiments indicated that a critical photoperiod induces diapause and an eventual reduction in sensitivity to photoperiod allows reproductive activity to resume.

A modelling analysis of the successful biological control of Sitona discoideus (Coleoptera: Curculionidae) by Microctonus aethiopoides (Hymenoptera: Braconidae) in New Zealand

Simple models were developed to explore the interaction between the lucerne (Medicago sativa L.) pest Sitona discoideus Gyllenhal and its introduced braconid parasite Microctonus aethiopoides Loan in New Zealand. A model for the population dynamics of S. discoideus demonstrated that observed levels of parasitism account for a decline in pest abundance, in spite of strong density-dependent mortality in the host. An empirical model for changes in parasitism from year to year, spanning five to six parasitoid generations each year, suggested that control is likely to be maintained in the long term and that the interaction is stable

An examination of the relationship between Argentine stem weevil Listronotus bonariensis (Kuschel)) and several of its host grasses

Abstract The susceptibilities of several New Zealand pasture grasses to Argentine stem weevil oviposition and larval attack were investigated. Short rotation cultivars of ryegrass showed higher susceptibility to both forms of attack than perennial ryegrass cultivars. It is possible that the latter are resistant to weevil attack because of their comparatively high cellulose levels and consequent toughness. Of the other grasses, tall fescue was found to be highly resistant to egg-laying whereas Timothy was found to be tolerant to larval mining. Larval survival of 30%–40% was estimated to occur between the egg and first instar stage in most grasses compared with the more variable and lower survival levels of 7%–23% between the first and second instars. These levels of survival were again proportional to relative cellulose levels. From the second instar onwards there was little or no larval mortality. The resistance to adult weevil feeding in the young seedlings of‘low cellulose’ (‘L.C.’) selection of ‘Grassl...

New Zealand pest management: current and future challenges.

New Zealand is under increasing pressure from terrestrial and aquatic pests, weeds and diseases that threaten the countrys ecosystems and economy. Ongoing improvement in existing pest management methodologies and novel approaches are required in response to public concerns about animal welfare, increasingly stringent trade requirements, abolition of groups of pesticides and resistance to existing pesticides as well as, possibly, biological control agents. Surveillance and pest monitoring are needed to increase the chances of early interception of invasive species or to confirm their eradication. Core capabilities in taxonomy, genomics, phenology, ecology, pest impacts, development of novel control tools and social science are required and must be maintained nationally. Given New Zealands unique environment, the ecology of invasive pests cannot be presumed to be the same as that in their native ranges, yet currently many pests in New Zealand are managed with poor understanding of their bionomics and impacts. Failure to address these areas will have serious adverse impacts on New Zealand.

Age-related susceptibility of lucerne to sitona weevil, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae), larvae and the associated patterns of adult infestation

Abstract Larval densities of Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) in lucerne stands in North Canterbury were found to decline on average by 40070 per year of crop growth. Conversely, there was no resultant weevil density/crop age relationship following the post-aestivatory autumn invasion of the stands by flying weevils. Thus the ratio of autumn immigrants to the pre-aestivatory emergent adults was deduced to be higher in older stands. Since the numbers of incoming autumn immigrants and resultant egg numbers showed no relationship to crop age density, it was also deduced that the observed decline in larval density with crop age was the result of relatively high survival of neonate larvae on young plants. This could have been caused by the nodules on the shallow root systems of the younger stands being more accessible to sitona larvae than the deeper roots of older stands. Plant density declined with increasing crop age but this was considered to have a negligible effect on the relations...

Predicting the Risk from Biological Control Agent Introductions: A New Zealand Approach

Since the publication of Silent Spring (Carson 1963) there has been increasing demand to reduce the amount of agricultural pesticides used. This need has been further supported by the development of increasing levels of pesticide resistance, and the market advantages for products from “sustainable” agricultural systems. Classical biological control, where a predator, parasite, or pathogen is imported to control a weed or pest, is one obvious alternative to pesticides and has often been promoted as environmentally safe (e.g., DeBach and Rosen 1991).

The bionomics of Listronotus bonariensis (Coleoptera: Curculionidae) in Canterbury, New Zealand

A study was conducted in 1990–1995 in Canterbury, New Zealand to describe the phenology and seasonal abundance of all stages of the Argentine stem weevil Listronotus bonariensis (Kuschel), a New Zealand pest of Gramineae. Of note were major fluctuations in the densities of all stages from one season to the next which were not explained directly in terms of the availability of Neotyphodium lolii -free ryegrass tillers. The overwintering mortality rates of L. bonariensis were found to be linear and remarkably similar between seasons and locations in the absence of pathogens. This study also showed that care must be taken in the use of existing data to analyse the impact of the recently introduced South American parasitoid wasp Microctonus hyperodae Loan as a biological control agent of L. bonariensis ; errors may exist because of earlier sampling biases. In spite of the confounding effects of seasonal variation in the L. bonariensis population, reduction in the size of the L. bonariensis first summer generation egg and larval peaks coincided with a build up of M. hyperodae .

Population dynamics and larval establishment of Sitona discoideus (Coleoptera: Curculionidae) in New Zealand lucerne.

(1) Sitona discoideus Gyllenhal population data collected from young lucerne (Medicago sativa L.) in Canterbury, New Zealand in 1982-86 were analysed using life tables. Manipulated weevil densities in 1983-84 allowed intra-seasonal and inter-seasonal relationships to be studied. (2) In general, there was a high degree of density-dependent mortality, probably amongst the neonate larvae during their establishment in the root nodules. (3) There was considerable variation in the pattern of larval survival in wet compared with dry seasons. In the latter, density-dependent effects occurred after little cumulative egg laying (750-2400 eggs m-2) compared with higher levels (11 770 m-2) in the wet season. Under wet conditions, there was greater mortality amongst the later instars. (4) Egg laying in the field was modelled on laboratory-derived temperature/rate relationships and field air temperatures. Model predictions suggested that 30-50% of the maximum fecundity was reached, indicating some maladaptation. (5) The range of feeding habits of Sitona spp. is reviewed with regard to the degree of dependence of the genus on root nodules.

The impact of invasive invertebrate pests in pastoral agriculture: A review

Abstract Non‐indigenous, invasive invertebrate pests have a detrimental effect on the New Zealand economy through impacts on pasture and forage production. Estimates of the economic impact have varied from