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, 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.

PCR gut analysis reveals thatTenuiphantes tenuis(Araneae: Linyphiidae) is a potentially significant predator of Argentine stem weevil,Listronotus bonariensis(Coleoptera: Curculionidae), in New Zealand pastures

“…In ryegrass (Lolium perenne L.) pasture, T. tenuis has been recorded in densities as high as 51.8 m (2 (Vink et al 2004), which suggests predation rates of up to 3.9 L. bonariensis m (2 per day. None of the 13 male T. tenuis tested positive for the presence of L. bonariensis DNA; however, a chi-squared test did not reveal a significant difference in the ratio of female and male positive results (x 2 02.891, v01, P00.0891).…”

“…Our estimates of predation rate are very preliminary, as they are based on DNA digestion rates reported for another prey species (Sheppard et al 2005) and the densities we used were from a previously study in Canterbury pastures (Vink et al 2004). Ideally, these rates and densities should be measured concurrently as part of a larger study; however, taking into account the assumptions we made, dense T. tenuis populations could potentially remove 3.9 L. bonariensis m (2 per day.…”

“…We did not measure densities for T. tenuis at the time of sampling, so we used figures from a previous study in Canterbury pastures (Vink et al 2004) as an estimate of possible density.…”

“…Tenuiphantes tenuis is a small (2Á2.5 mm body length) spider that is widespread and common throughout New Zealand, particularly in the South Island (Millidge 1988). It is found in high numbers in pasture and arable crops (Martin 1983;Millidge 1988;Sivasubramaniam et al 1997;Topping & Lo¨vei 1997;McLachlan & Wratten 2003;Clark et al 2004;Vink et al 2004) and also occurs in disturbed native forest and pine plantations (Millidge 1988). In Canterbury, it is the numerically dominant spider species in agricultural habitats (Sivasubramaniam et al 1997;McLachlan & Wratten 2003;Vink et al 2004) where it occurs in higher numbers than other arthropod predators (Sivasubramaniam et al 1997).…”

“…In Canterbury, it is the numerically dominant spider species in agricultural habitats (Sivasubramaniam et al 1997;McLachlan & Wratten 2003;Vink et al 2004) where it occurs in higher numbers than other arthropod predators (Sivasubramaniam et al 1997). Up to 79 T. tenuis m (2 have been found in pasture in Canterbury (Vink et al 2004). Despite the abundanceofT.tenuisinNewZealandagroecosystems, nothing is known about what it feeds on there.…”