Effect of anthesis on prey availability at linyphiid spider webs and implications for transgenic crop risk-assessment

Dietary diversification, including consumption of plant tissues such as pollen, can enhance the fecundity of generalist predators, resulting in improved control of pest prey. Supplemental pollen feeding has been observed in many natural enemies, including spiders. Linyphiidae represent a major component of food webs in agroecosystems; their horizontal, ground-level webs have the potential to intercept pollen grains during anthesis of crop plants, providing the opportunity for pollenivory to occur. Furthermore, transgenic Bacillus thuringiensis corn expresses insecticidal proteins in pollen, posing an exposure risk to non-target arthropods. To measure pollen and prey interception in simulated linyphiid webs, a 20x20m miniature sticky traps grid was established within and downwind of a corn agroecosystem. Traps were exposed for 24 hours, collected, and replaced with additional traps for 28 consecutive days in July and August 2008, to encompass periods before, during and after anthesis. In 2009, prey interception rates at websites and non-websites were recorded over the season. Over 150,000 corn pollen grains and 5,000 prey items (dominated by Collembola and Hemiptera) were intercepted at simulated websites. Dates of peak anthesis resulted in pollen counts as high as 4,000 grains per website in the interior of the cornfield. SADIE (Spatial Analysis by Distance IndicEs) indicated significant temporal and spatial variability in pollen interception within and outside the corn field. These results revealed potential for dietary supplementation with pollen in ground-based sheet-web spiders indicating that pollenivory may be an important component of the feeding biology of linyphiids, as well as risk-assessment of genetically modified crops.