Effects of the wasp-spider, Argiope bruennichi, on planthoppers and leafhoppers
The role of spiders as generalist predators of herbivores is an important issue for prey population dynamics and spatial distribution. We conducted a field experiment in order to study the effects of the web-building spider Argiope bruennichi on plant- and leafhoppers in a grassland habitat. Spider densities were manipulated through repeated removal in open plots that were separated by mown strips, and effects on Auchenorrhyncha were recorded in two blocks of different plot sizes by suction sampling. We found significant negative effects of A. bruennichi on the abundance and biomass of their prey in both blocks. The most abundant planthopper Delphacodes venosus was most severely affected. However, this species is strictly epigeic, and therefore, predation through a web-building spider is unlikely to be the main cause for its decline. We suggest that non-lethal effects of spiders could be an important factor for the dynamics of herbivore communities in grassland foodwebs.