PREY CONTROL BY AN ASSEMBLAGE OF GENERALIST PREDATORS - SPIDERS IN GARDEN TEST SYSTEMS

The hypothesis that generalist predators limit associated prey populations was tested using spiders. Two habitat manipulations (addition of mulch and flowers) were used to enhance spider numbers in a mixed vegetable system. Significantly higher spider densities were observed in the plots to which mulch alone or both mulch and flowers had been added. Insect damage to the plants was significantly lower in the plot to which mulch had also been added, which correlates with the lower numbers of pest insects in plots containing mulch. That spiders were the probable cause of the effect was demonstrated. Spiders were added to a subset of bagged broccoli plants that had been infested previously with known numbers of herbivorous pests. Plant damage in bags lacking spiders averaged 93.3%; damage averaged 31.8% in bags in which spiders had been added. -from Authors