Host spatial pattern influences induction of parasitization by Trichogramma (Hymenoptera : Trichogrammatidae)

The influence of host intrapatch spatial distribution on parasitoid host ac ceptance behavior was investigated with Trichogramma principium parasitizin g eggs of grain moth, Sitotroga cerealella. Single females were placed in P etri dishes, each containing 60 host eggs arranged either as a compact patc h or partitioned into 60 or 12 clusters each consisting of 1 or 5 eggs, res pectively. Partitioned patches provoked parasitization more often than comp act patches. The percentage of ovipositing females (i.e., females parasitiz ing at least one of 60 host eggs) increased with the number of clusters, wh ile it was independent of the intercluster distance over intervals of 2.5-1 5 mm. The mean number of eggs parasitized by ovipositing females during 48 h was almost independent of the host egg spatial pattern. As a result, the rare of parasitization was higher when the hosts were sparsely distributed within a patch than when they were aggregated.