Foraging Behavior of Aphidius ervi (Haliday) (Hymenoptera: Braconidae: Aphidiinae) at Different Spatial Scales: Resource Utilization and Suboptimal Weather Conditions

The effect of habitat structure and adverse weather conditions on the foraging behavior and resource utilization of Aphidius ervi (Haliday), a parasitoid of the pea aphid Acyrthosiphon pisum (Harris), was analyzed at two different spatial scales. Oviposition of A. ervi females was generally low, ranging between one and four eggs laid per aphid colony (colony size 10 aphids). On isolated host plants, the foraging success of A. ervi females was not influenced by simulated “rain” compared to standard conditions. In contrast, simulated “wind” increased the number of ovipositions and the oviposition rate because fewer aphids dropped off plants during parasitoid attack. Parasitoid dispersal was not prevented by adverse weather conditions. Within a patch of host plants (= plant canopy), A. ervi females visited most host plants under standard conditions. Only parasitoids that had oviposition experience on the release plant successfully found new hosts after dispersal. In contrast to isolated plants, simulated “wind” and “rain” reduced both parasitoid dispersal and the oviposition rate, demonstrating the importance of habitat structure for the parasitoidʹs foraging behavior.