Simple SummaryNatural enemies of major pests such as parasitoids require sugar-rich food for development and reproduction. In agricultural fields, honeydew excreted by aphids is often the predominant sugar source that parasitoids can consume. Moreover, honeydew can constitute a cue used by parasitoid females to find their aphid host. However, in some species, such as the woolly apple aphid (Eriosoma lanigerum), honeydew is coated with a thin layer of wax, which could make its consumption harder and prevent the emission of attractive odors for parasitoids. In the present study, we evaluated the benefits in terms of longevity and host searching that could provide honeydew to the main parasitoid of the woolly apple aphid,Aphelinus mali, and infer parasitoid feeding patterns in apple orchards. Results suggested thatA. maliis able to consume honeydew in laboratory and field conditions and to benefit from honeydew, as it increased its longevity when honeydew was provided with water. Although no olfactory preference was observed, honeydew also stimulated oviposition byA. mali. The contribution of honeydew to increase the efficiency ofA. malias a biological control agent is discussed.AbstractMany parasitoids need to feed on sugar sources at the adult stage. Although nectar has been proven to be a source of higher nutritional quality compared to honeydew excreted by phloem feeders, the latter can provide the necessary carbohydrates for parasitoids and increase their longevity, fecundity and host searching time. Honeydew is not only a trophic resource for parasitoids, but it can also constitute an olfactory stimulus involved in host searching. In this study, we combined longevity measurements in the laboratory, olfactometry and feeding history inference of individuals caught in the field to test the hypothesis that honeydew excreted by the aphidEriosoma lanigerumcould serve as a trophic resource for its parasitoidAphelinus malias well as a kairomone used by the parasitoid to discover its hosts. Results indicate that honeydew increased longevity ofA. malifemales if water was provided. Water could be necessary to feed on this food source because of its viscosity and its coating by wax. The presence of honeydew allowed longer stinging events byA. malionE. lanigerum. However, no preference towards honeydew was observed, when given the choice. The role of honeydew excreted byE. lanigerumonA. malifeeding and searching behavior to increase its efficiency as a biological control agent is discussed.