Clover root weevil (Sitona lepidus) in New Zealand: the story so far

Abstract

The rapid spread of clover root weevil (Sitona lepidus) (CRW) since its introduction in the early 1990s, threatens the competitive advantage of New Zealand's pastoral industry. When CRW was discovered, it had already spr ead too far for containment. The insect's distribution currently covers the North Island and there is no reason to prevent its spread ultimately throughout NZ. With no competing species, CRW is more damaging in NZ than in its native Europe. Clover root weevil affects white clover nitrogen (N) fixation while simultaneously reducing the clover content of pastures thereby lowering total forage quality. Legume germplasm was screened for resistance/tolerance and while no resistance was discovered, vigorous growing white c lover plants showed tolerance to CRW and gains from selection for tolerance were achieved. Eliminating remnant clover before pasture renovation or growing a crop between grass stages reduces the resident CRW population and improves clover re-establishment. However, CRW can reinvade and potentially return to its original density. Two candidate biological control agents are being pursued for release later in 2005. Clover root weevil's impact on pastoral farming varies, partially due to environmental variation, which dictates clover growth and CRW development. Keywords: clover root weevil, cultivar selection, life cycle analysis, pasture management, Sitona lepidus

Quantifying the economic cost of invertebrate pests to New Zealand’s pastoral industry

“…The 1996 discovery of CRW in New Zealand (Barratt et al 1996), its subsequent spread throughout the North (Gerard et al 2011) and South Islands of New Zealand (Ferguson, McNeill et al 2012), the impact on white clover in pastures (Eerens et al 2005;Gerard et al 2007) and its potential economic cost (Wear and Andrews 2005;Nimmo-Bell 2009;Basse et al 2015;Hardwick et al 2016) are well documented. It was the most significant invasive pasture pest to establish in New Zealand since black beetle in the 1930s, and the only one to achieve nationwide major pest status since the arrival of ASW early last century.…”

“…High numbers of CRW can reduce clover levels in the pasture (Willoughby and Kettlewell 1998). This in turn results in pastures characterised by poor production and depleted forage quality (Willoughby and Addison 1997;Eerens et al 2005).…”

Managing biological succession in intensive pastoral ecosystems for improved production and sustainability

“…and Tasmanian grass grub (Acrossidius tasmaniae) are considered to be associated with run-out pasture. Of these insect pests, clover root weevil, Argentine stem weevil and grass grub are potentially the most widespread and important in New Zealand pastoral systems (Eerens et al 2005;Goldson et al 2005). Currently, clover root weevil is found in pastures throughout the North Island and its presence has been confirmed in the Nelson and Canterbury regions of the South Island (Eerens et al 2005;C.B.…”

Response to clover root weevil outbreaks in South Canterbury, Otago and Southland; the agricultural sector and government working together

“…Adults of CRW feed on white clover leaves and can reduce establishment of seedlings, but it is the rootfeeding larvae that cause most damage by reducing nitrogen fixation and weakening or killing plants (Barratt et al 1996 and references therein;Eerens et al 2005;Gerard et al 2007). To maintain production, farmers may apply additional nitrogen fertiliser, grow more non-susceptible forage plants, and/or increase supplementary feed (White & Gerard 2006).…”