Relative dispersal ability of a key agricultural pest and its predators in an annual agroecosystem

In predator–prey interactions, a widely held view is that prey species have higher dispersal rates relative to their predators and are thereby able to escape from predation by colonizing habitats before their predators. Despite major implications for predator–prey interactions, community assembly, and biological control, this view has rarely been tested, and measuring relative dispersal abilities is often complicated by colonizing predators and prey originating from different locations. In California’s San Joaquin Valley, the periodic harvest of alfalfa presents an opportunity to measure dispersal of a key generalist pest, Lygus spp., relative to a suite of its generalist predators. We performed a large-scale mark-capture study by marking a mature alfalfa field containing Lygus and its predators with an aerial application of a protein marker. The alfalfa was then harvested by the grower, prompting a dispersal event. At several times following harvest, surrounding cotton fields were sampled at known distances from the marked field to quantify movement by Lygus and its predators. Contrary to the general view, our data do not suggest that Lygus routinely out-disperses its suite of predators. Instead, the mean dispersal distance for Lygus fell near the average dispersal distances of its predators. Implications for biological control are discussed in light of these results, and the importance of predators’ trophic strategy is stressed.