Impact of clover root weevil Sitona lepidus (Coleoptera: Curculionidae) larvae on herbage yield and species composition in a ryegrass-white clover sward.

The effects of root herbivory at five densities of Sitona lepidus larvae (overall means between 4 and 333 larvae m-2) were assessed over 2 years on newly established perennial ryegrass-white clover swards in a small plot trial. Initial larval establishment in autumn 2003 was positively related to clover content in plots, and there was no significant impact on clover herbage yield in the first year. Nodule damage in winter 2003 increased with larval density, and results suggested an overcompensatory response in nodule production. A 34-35% reduction in clover yield between highest and lowest S. lepidus densities was recorded for both cultivars in the second year, with greatest losses in spring 2004. This coincided with reductions in clover root and stolon weights. Plant parasitic nematodes and grass grub larvae were most abundant in the plots with lowest weevil numbers. These results confirm field observations that S. lepidus is a major pest of pastures. [ABSTRACT FROM AUTHOR]