Honeydew Is a Food Source and a Contact Kairomone for Aphelinus mali

Abstract

Many 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 aphid Eriosoma lanigerum could serve as a trophic resource for its parasitoid Aphelinus mali as well as a kairomone used by the parasitoid to discover its hosts. Results indicate that honeydew increased longevity of A. mali females 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 by A. mali on E. lanigerum. However, no preference towards honeydew was observed, when given the choice. The role of honeydew excreted by E. lanigerum on A. mali feeding and searching behavior to increase its efficiency as a biological control agent is discussed.

Keywords: Eriosoma lanigerum; biological control; chemical cues; parasitoids; sugars.

Figure 1

Longevity of A. mali either exposed to different food sources (honeydew, honeydew with water, and water) or starved. Letters above the bars indicate results of the post hoc Tukey test.

Figure 2

The foraging behavior of A. mali exposed to honeydew of E. lanigerum or water. The total time spent stationary, moving, stinging-oviposition, attacking or feeding as well as the total time spent at the base of the arena with the food and host sources or at the walls.

Figure 3

Time spent in each branch of an olfactometer by A. mali emerged from E. lanigerum when given a choice between two stimuli (Honeydew-Room air: (A); Honeydew-Water: (B); Water-Room air: (C)). The time spent in the central area corresponds to those parasitoids with undetermined choice [31]. Letters above the bars indicate results of the post hoc Tukey test.

Figure 4

Estimated relative frequencies of A. mali females from each feeding class (diluted honey, honeydew, nectar, starved and water) for two sampling dates (February and March). Results were obtained using a Random Forest algorithm followed by the Adjusted Counting prevalence estimation method that classifies field-collected parasitoids.