The use of mulch to increase Spider (Arachnidae) numbers; a habitat approach to biological insect control

Summary

The potential for insect predators to contribute to a biological balance of insect species was explored with mulch. Insects were collected in pitfall traps in outdoor microplots over 3 seasons in southern Ontario, Canada. Treatments varied each season with crops of oats or soybeans, with residue of straw, corn stalks or paperfibre, and with residue tilled in or surface applied. In 2006 at the peak of spider population density there was a significant effect of the plant and the paperfibre residue on increasing spider density. Existing data sets on spiders by Spiller and Schoener (1988 & 1994) were analyzed to assess the potential to increase spider survival from improved carrying capacity of their habitat. Spider census data was tested with curve fitting models in Aikaike Information Criteria (AIC). Spider populations of Metepeira, with sizeable numbers, were density dependent. Demographic data was assembled from Spiller & Schoener, 1988 and population size was projected with RAMAS Ecolab. Increasing the carrying capacity increased spider populations in the model projections. Mulch improves spatial diversity and could increase spider density from reduced intraspecific competition in the plot experiments. Increasing spider numbers with habitat complexity in agricultural systems could allow spiders to reduce specific pest problems through maintaining the balance of insect species.