Diurnal distribution of the money spider Atypena formosana in the rice plant and its relation to tiller density

Abstract

The diurnal vertical distribution of spiders is of interest to understand which prey types Atypena formosana (Araneae: Linyphiidae) may encounter over the course of 24 h. In this study, we visually assessed the diurnal distribution of A. formosana in rice plants and the effect of tiller number on spider number. Field samplings were done at the IRRI experiment station on clear sunny days with little wind. Initially, we sampled (by using a sweep net) A. formosana at the panicle initiation stage of IR72 at 50 days after transplanting (DAT) on 23 Sep 1999. Temperatures ranged from 23.0 to 31.8 °C, with an average (±SD) of 28.5 ± 3.2 °C, and relative humidity (RH, ±SD) was 74 ± 13.8%. Sweep netting provides a fast and useful indirect measure of diurnal changes in the proportion of the spider population in the upper portion of the crop, but it is less efficient in sampling arthropods at the lower level. Ten sweep-net samples, each consisting of 10 sweeps, were taken four times over a 24 -h period (0600 h, noon, 1800 h, and midnight). We sampled the field diagonally, avoiding sampling any location twice.