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