Searching behavior of an aphid parasitoid and its hyperparasitoid with and without floral nectar

While enhancing the searching ability of a natural enemy can give a major improvement in host population suppression, it is important to demonstrate selectivity in favor of the third trophic level when changes, such as added floral resources, are made to agro-ecosystems to enhance biological control efficacy. To explore this question, a pea-aphid endoparasitoid, Aphidius ervi, and its hyperparasitoid, Dendrocerus aphidum, were used to test the effects of prior feeding with buckwheat nectar on searching behavior of both the parasitoid and hyperparasitoid. Digital video was used to record behavior and data were scored and analyzed using Observer Video-Pro software. A. ervi females in nectar treatments spent a higher proportion of their time actively searching than those with access to water only. Fed parasitoids antennated, stung and groomed significantly more than unfed female parasitoids, and spent almost twice as much time attacking and carried out nearly twice as many attacks as unfed parasitoids. D. aphidum spent the greatest proportion of time attacking potential hosts in both 'fed' and 'unfed' treatments. However, although fed females spent a significantly longer time antennating, there was no significant difference in walking or grooming between treatments. Unfed female hyperparasitoids spent significantly more time stationary than fed females. The results demonstrate that the searching efficiency of both third and fourth trophic level parasitoids is enhanced by access to floral nectar. Nectar provision can therefore potentially have positive or negative effects on biological control, depending on the relative proportion of each species. (C) 2011 Elsevier Inc. All rights reserved.