Some effects of grass grub <i>(Costelytra zealandica (White))</i> larvae on pasture plants

Abstract

Abstract Four experiments in small containers investigated the effects of third‐instar larvae of Costelytra zealandica (White) on pasture plants: 1.Where larvae had a choice of twc&gt; species of pasture plants there was little evidence of migration from one species to another. Larval survival was much greater under clovers than under grasses. 2.When perennial ryegrass ( Lolium perenne L.), browntop ( Agrostis tenuis Sibth.), Yorkshire fog ( Holcus lanatus L.), and white clover ( Trifolium repens L.) were grown as monocultures on pumice, 10 larvae/sq ft significantly reduced plant growth, and 30 larvae/sqft produced greater damage. Young white clover plants were most susceptible to damage, followed by browntop, then perennial ryegrass and Yorkshire fog. Ten larvae/sq ft produced severely damaged plants for 30 to 40 days after grub introduction, and 30 larvae/sq ft produced damage for up to 50 days after grub introduction. 3.White clover monocultures grown on pumice were completely destroyed by 40 larvae/sq ft, but white clover grown with perennial ryegrass was ler.s susceptible. Larval mortality was greater in the white clover/ryegrass mixture. 4.Perennial ryegrass monocultures grown in pumice with cow dung as additional organic matter showed only slight damage with up to 40 larvae/sqft. In the absence of additional organic matter, severe plant damage was caused by 20 and 40 larvae/sq ft. Little damage was found with 10 larvae/sqft.