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New Zealand's economically vital exotic pastures are unique in their low complexity making them highly susceptible to invasive pest species such as the Argentine stem weevil Listronotus bonariensis. This field-based contribution further examined the ecology of the adult weevil and its parasitoid control agent Microctonus hyperodae. This included factors that affect field sampling accuracy, interpretation of population density and parasitism estimates. Compared to adult population estimates measured via turf flotation, suction sampling (G-vac) showed c.30% under-estimation of population densities while parasitism rates were over-estimated by c.26%. The bionomic implications of the sampling biases are discussed as they relate to the recently observed sharp declines in L. bonariensis parasitism. The weevil's field parasitism rates showed no relationship to population density again confirming the parasitoid's very high host searching efficiency. This study also coincided with meteorological conditions (>30°C) that resulted in a very large L. bonariensis 'swarming' event. The mass emigration from the experimental plots left only a low residual population of parasitised weevils that typically do not fly. Therefore, measured L. bonariensis populations and their M. hyperodae parasitism levels cannot always be presumed to be solely the result of population dynamics in situ. [ABSTRACT FROM AUTHOR]

In identifying endophytes for use in pastures in New Zealand there have been two strategies used, either exclusion of ergopeptine and lolitrem alkaloids or, retaining some ergopeptine expression to enhance the stability of natural defences against invertebrate pests. Both have their strengths and weaknesses. It is a matter of balancing these to ensure the end-user has access to a product that satisfies their needs – a persistent pasture with low to nil animal toxicity in terms of animal production and welfare. The range and intensity of ergot alkaloids in grazed pasture on both pasture and ruminants is reviewed, with emphasis on New Zealand. Ergot alkaloids associated with pasture are produced by associations between certain Epichloë endophyte strains and temperate grasses. Ergot alkaloids have been shown to improve persistence of pasture through providing resistance/deterrence to insect pests as well as deterring grazing animals. However, ergovaline is toxic to grazing animals. Some commercially available ryegrass-endophyte associations can produce ergovaline concentrations close to those found in associations between ryegrass and the standard endophyte. It is feasible to eliminate ergot alkaloids from pasture grasses in New Zealand as endophyte strains are commercially available that do not express ergovaline and yet still provide excellent pest resistance. [ABSTRACT FROM AUTHOR]

The invertebrate pests most commonly affecting New Zealand's pastoral-based production in 'average' years cause losses of between $1.7B and $2.3B p.a. of which up to $0.9B occur on sheep and beef farms and $1.4B on dairy farms. The native scarab grass grub is the most costly pest causing losses of $140-380 M on dairy farms and $75-205 M on sheep and beef farms annually. The exotic scarab, black beetle, although only affecting approximately 1 M ha, costs dairy farmers up to $223 M and sheep and beef farmers up to $19 M annually. Porina cause losses up to $84 M and $88 M respectively. Pasture nematodes are estimated to cost up to $274 M p.a. for dairy farmers and $326 M p.a. for sheep and beef farmers. Two exotic pests, Argentine stem weevil (ASW) and clover root weevil (CRW) are causing damage estimated at up to $200 M p.a. and $235 M p.a. respectively in dairy and sheep and beef pastures. While CRW is subject to successful biological control management it still causes considerable losses. Lesser pests also contribute to lost production, particularly as they often coexist with more major pests. However, their economic cost to New Zealand is difficult to calculate due to the variable nature of infestations on both temporal and spatial scales. At farm and paddock level, it is abundantly clear that substantial savings could be made if pest management is achieved. It is equally clear that in many instances the tools to do so are limited but if developed would contribute substantially to farm profitability. [ABSTRACT FROM AUTHOR]