Effect of plant structure, host density and foraging duration on host finding by Trichogramma evanescens (Hymenoptera:Trichogrammatidae)

While searching for hosts on plants, female parasitoids meet different plant structures and host densities that will influence their host finding success. In this study, we determined whether plant structure, host density, and foraging duration influenced the percentage of Ephestia kueliniella Zeller eggs parasitized by Trichogramma evanescens Westwood. One female was introduced to forage either 4 or 24 h on artificial plants of three different structures (simple, intermediate, and complex) on which 4 or 16 host eggs were glued. Plant structure influenced rate of parasitism in both foraging durations, whereas host density was found to be significant only when female had 4 h to forage. Mean rate of parasitism generally decreased with an increase in complexity of plant structure and host density in both foraging durations. Almost twice as many eggs were parasitized on simple plants compared with complex plants for all host densities and foraging durations. Overall, female parasitoids parasitized, on average, <1 egg/h, except when they foraged 4 h in the presence of 16 eggs. Plant structure therefore affects host-encountering success. Physical structure of a plant mediates ecological interactions and is involved in parasitoid-host population dynamics. It operates by increasing costs associated with host finding.