Foraging behavior of field populations of Diadegma spp. (Hymenoptera: Ichneumonidae):: Testing for density-dependence at two spatial scales

The foraging behavior of populations of Diadegma spp. (Hymenoptera: Ichneumonidae) attacking the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), was studied in the field. The effect of host density on percentage parasitism was investigated at two spatial scales: that of the individual plant, as well as a "cluster of plants" at low, medium and high densities. Using binoculars, parasitoid searching was observed on host plants at different host densities over an 8-h period. Behavior was compared to that predicted under the Patch Selection Theory. Percentage parasitism was independent of host density at both spatial scales. However, the behavioral studies showed parasitoid aggregation behavior at higher host densities. The population displayed an imperfect preference for higher host densities in the first 4 h of foraging. In the second 4-h period, no preference was observed.