Effects of plant species and fertilisers on grass grub larvae,Costelytra zealandica

Abstract

Abstract Laboratory feeding studies have confirmed that ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.), white clover (Trifolium repens L.), and red clover (Trifolium pratense L.) are favourable host species, and lucerne (Medicago sativa L.) an unfavourable host species, for third-instar grass grub (Costelytra zealandica (Whitej) larvae. A Wairakei ecotype of Yorkshire fog (Holcus lanatus L.) was favourable and ‘Grasslands Wana’ cocksfoot (Dactylis glomerata L.) unfavourable for third-instar larvae. When feeding on mixtures of white clover and cocksfoot or ryegrass and lucerne roots, larvae selectively fed on the favourable pasture species. Addition of NPK fertiliser to the pasture plants had little effect on larval growth rate and survival in laboratory and small plot trials. There was no consistent change in consumption rates in response to increasing NPK (15 : 7 : 5) fertiliser. Addition of N (urea) and P (superphosphate) to field populations had little or no effect on grass grub population density during 1982–84. Larval survival (April–October) and pupal weight were not related to Nand P levels in the foliage.