Floral Resources Effect on the Longevity of the Aphid Parasitoid Aphidius erviHaliday ( Hymenoptera : Braconidae ) and its Hyperparasitoid Alloxysta VictrixWestwood ( Hymenoptera : Charipidae )

Abstract

Changing biodiversity can impact higher trophic levels, which may in turn influence food-web structure and ecosystem functioning. In this study, some floral resources were evaluated in the laboratory to assess their effect on the longevity of the fourth-trophic-level parasitoid Alloxysta victrix Westwood (Hymenoptera: Charipidae), which parasitises aphid parasitoids. When the hyperparasitoid was exposed to flowering buckwheat (Fagopyrum esculentum Moench cv. Katowase) or coriander (Coriandrum sativum L. cv. Slowbolt), it survived ten times longer than it did when fed on water only and five times longer with phacelia (Phacelia tanacetifolia Bentham cv. Balo) or sweet alyssum (Lobularia maritima L. cv. Carpet of Snow). Aphidius ervi Haliday (Hymenoptera: Braconidae) 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 as those in the control. These results indicate that floral resources deployed in conservation biocontrol should also be screened for their effects on the fourth trophic level. Modelling or field-cage experiments could be useful in elucidating the possible population and community consequences of deploying floral resources in agro-ecosystems to enhance biological control effectiveness.