Aphid infestation induces plant sex-specific changes in floral chemistry and pollinator behaviour in <i>Silene latifolia</i>

Pollinators share the complex information and resource landscape of their host plants with herbivores. Yet, how sap feeders affect floral attractiveness to pollinators remains poorly understood, despite the critical role of this tripartite interaction in natural and agricultural ecosystems. In dioecious plant species, which display pronounced sexual dimorphism, these intricate interactions may vary in magnitude and direction between females and males, with significant implications for plant population dynamics and species co-evolution. In this study, we examined how infestation by the oligophagous aphid Brachycaudus lychnidis affects sex-specific interactions between the dioecious plant Silene latifolia and its specialist moth pollinator Hadena bicruris. We exposed male and female plants to aphid herbivory and evaluated its effects on floral traits (visual cues, floral scent, and nectar chemistry) and pollinator behaviour. While aphid infestation affected some floral traits equally in both sexes and others more strongly in males or in females, we observed stronger declines in female attractiveness to pollinators, which were mainly linked to nectar compounds potentially acting as feeding cues or behavioural modulators. We discuss our results in the light of sexual selection and plant defence theory while emphasizing the complementarity of female and male traits in stabilizing this specialized plant-pollinator-herbivore system.