Floral diversity, parasitoids and hyperparasitoids - A laboratory approach

摘要

Adding floral resources to agro-ecosystems to improve biological control can enhance the survival, egg load, and parasitism rate of insect parasitoids. However, this may not always be the case because the herbivore may benefit from the added resource as much as, or more than the third-trophic level. In addition, the natural enemies of those in the third-trophic level may also derive improved fitness from the added resources. Both these processes will dampen trophic cascades, leading to less-effective biological control. In this study, the effect of adding different flowering plants on the longevity, egg load, aphid parasitism rates and hyperparasitism of Aphidius ervi Haliday (Hymenoptera: Braconidae) by its hyperparasitoid Dendrocerus aphidum Rondani (Hymenoptera: Megaspilidae) were investigated, using the pea aphid Acyrthosiphon pisum Harris (Homoptera: Aphididae) as the herbivore. Parasitoids exposed to buckwheat survived, on average, between four to five times as long as those in the control (water) and those in phacelia, alyssum and coriander treatments survived three to four times as long. Hyperparasitoids exposed to buckwheat survived five to six times as long as those in the control and three to five times longer with the other plants compared with the control. Almost all flower species significantly increased parasitoid and hyperparasitoid egg loads and the number of parasitised aphids and parasitised mummies compared with control. Understanding the factors influencing the dynamics of multitrophic interactions involving flowering plants, herbivores, parasitoids and hyperparasitoids is a fertile area for future research. One of the most challenging areas in contemporary ecology concerns the relative importance of different types of biodiversity mediating trophic interactions and thereby influencing the structure of communities and food webs. This paper begins to explore this using an experimental, laboratory-based approach.