Spiders (Araneae) and harvestmen (Opiliones) in arable crops and grasses in Canterbury, New Zealand

Abstract

As an initial step in assessing the impact of spiders and harvestmen as biological control agents for insect pests of arable crops, the population density and species richness of spiders and harvestmen were examined in a range of cereal crops and grasses at two sites in Canterbury, New Zealand, in 1996, 1997, and 1999 using a ground suction sampler. Twenty spiders (Order Araneae) and one harvestman (Order Opiliones) were identified from the grass and cereal samples. Thirteen were endemic species. Population densities were estimated in ryegrass, fescue, cocksfoot, prairie grass, wheat, and barley. Greatest population density and species richness were found in fescue and ungrazed ryegrass, in which mean densities of up to 180.8 spiders and harvestmen per square metre were recorded. Estimates of density and species richness were much higher in grasses than in cereals. The introduced linyphiid spider Tenuiphantes tenuis (Blackwall), comprised over half of the spiders and harvestmen sampled. Other commonly found species were the introduced money spider (Erigone wiltoni Locket), and the endemic wolf spider Anoteropsis hilaris (L. Koch). The introduced harvestman Phalangium opilio L. was also common.