Reproduction and dispersal pattern of egg parasitoids of Riptortus pedestris (Hemiptera: Alydidae) after installing pheromone traps plus non-viable host eggs

The aggregation pheromone of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) has a kairomonal effect on its egg parasitoids. The addition of non-viable R. pedestris eggs to aggregation pheromone traps was suggested as a means to enhance reproduction of parasitoids attracted to pheromone traps and was found to enhance field parasitism. In this study, we tested if the eggs added to traps are indeed used by parasitoids for their reproduction. Spatial distributions of egg parasitism were assessed in a barley and a sesame field where non-viable host eggs were installed at four distances (8, 16, 24, and 32 m) in two directions from the aggregation pheromone traps placed in the center of each field. While field parasitism increased significantly over time, it decreased with distance from traps. Higher egg parasitism was found up to 16 m from the point of release in both barley and sesame fields. To compare temporal changes in parasitism, traps were also installed in another barley and another sesame field without adding host eggs. From regression slope comparisons, significant differences were found only in the sesame fields, where the parasitism rate on the last sampling date in the egg-released field was higher than the comparison field by 80%. A higher male proportion was found near the trap installation point only for Gryon japonicum (Ashmead) (Hymenoptera: Platygastridae) in the sesame field. These findings suggest that supplemental host eggs in traps enhance field parasitism by increasing the reproduction and dispersion of field populations of parasitoids.