Effects of habitat type and spatial scale on density dependent parasitism in Anagrus parasitoids of leafhopper eggs

The ability of parasitoids to maintain a high rate of parasitism under varying conditions is considered crucial to their ability to control the populations of their hosts. Here, I tested parasitism rate by Anagrus parasitoids and its dependency on the density of Erythroneura leafhopper eggs at two spatial scales (leaf and field) and two habitat types (natural vs. agricultural). The rate of parasitism differed among field sites, increased across the season, and was similar in natural and agricultural sites. At the leaf scale, the rate of parasitism was density-independent or inversely density-dependent, consistent with a weak aggregation of parasitoids on leaves with high host densities and with limited oviposition-rate or egg supply. At the field scale, in contrast, parasitism rate was positively dependent on host density, which may be explained by demographic processes, such as higher recruitment and higher fecundities of females in host-rich field sites. Overall, the results demonstrate that parasitism patterns are highly dynamic in time and space and depend on the scale of observation.