Floral resources enhance aphid suppression by the hoverfly Eupeodes fumipennis

The reduction in floral diversity that often accompanies agricultural intensification may compromise the effectiveness of many natural enemies. Making the link between the presence of floral resources and the suppression of herbivores in crop fields has proved difficult, however. We investigated the effects of the floral resource plant sweet alyssum on aphid suppression by the hoverfly Eupeodes fumipennis Thompson (Diptera: Syrphidae) in California lettuce fields. The presence of alyssum in field cages significantly enhanced hoverfly egg production, resulting in more hoverfly larvae and fewer aphids. Hoverfly survival was unaffected by alyssum, indicating that the indirect effect of alyssum on aphids was mediated entirely through the reproductive component of hoverfly fitness. Alyssum and other plants species are used to enhance resources for natural enemies in agricultural landscapes, and the results of this study provide some of the clearest evidence to date that increasing floral resource availability can enhance pest suppression and crop quality through elevated natural enemy fitness.