Effect of native weevils (Coleoptera: Curculionidae) on white clover establishment and yield in tussock grassland

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Abstract
A trial was carried out in unimproved tussock grassland on the East Otago Plateau of the South Island of New Zealand to investigate the impact of native broad-nosed weevils (Coleoptera: Curculionidae) feeding on survival, establishment, and yield of oversown white clover. The trial consisted of 20 sites 1 km apart where two plots were established in each of 5 consecutive years. At each of the sites in each year, one of the plots was sprayed with parathion at 2-weekly intervals from September to December to allow seedlings to establish in “insect-free” conditions. The other plot was left untreated. The plots were sown in October and, by late December, seedlings suffered on average 40 and 6% mortality in the untreated and sprayed plots respectively. Sublethal insect feeding reduced nodulation on average by 46% and final established plant density by 39% in the unsprayed plots. Despite identical treatment of the two plots after the initial 3 months, white clover yields were significantly higher in the plots initially protected from insects where on average 58% more clover dry matter (an increase from 87 to 137 kg/ha per year) was produced over 5 years of harvesting the plots.

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