Association between omnivorous Orius bugs and their thrips prey at different spatial scales of Verbesina encelioides flowers

While many field studies have estimated the numerical response of predator populations to their prey, little is known about the numerical response of omnivores, especially at different spatial scales. We sampled populations of omnivorous Orius bugs and their thrips prey in Verbesina encelioides flowers at three hierarchical spatial scales; a flower, a small patch of plants (2 m diameter), and a large patch of plants (6 m diameter). Omnivore and prey densities were correlated using hierarchical statistic models. Data show that while prey was aggregated at the flower scale, adult omnivores were distributed uniformly at that level. These results suggest that antagonistic intraguild interactions may be shaping omnivore distribution at the smallest scale studied. The correlation between omnivore and prey densities was scale-dependent. Density of Orius nymphs was positively correlated with prey density at all spatial scales, but the density of adult bugs was positively correlated with prey density only at the largest scale. Results obtained here and from a companion study suggest that female bugs aggregate and lay more eggs where prey is more abundant. Differential mobility of Orius adults and nymphs may therefore underlie observed differences in omnivore-prey association at different spatial scales. Future studies should explore effects of plant materials on the aggregative response of omnivores to variation in prey density.