Assessing the impact of natural enemies of plant and animal pathogens on their host's population dynamics is needed to determine the role of hyperparasites in affecting disease dynamics, and their potential for use in efficient control strategies of pathogens. Here we focus on the long-term study describing metapopulation dynamics of an obligate pathogen, the powdery mildew (Podosphaera plantaginis) naturally infecting its wild host plant (Plantago lanceolata) in the fragmented landscape of the Åland archipelago (southwest Finland). Regionally, the pathogen persists through a balance of extinctions and colonizations, yet factors affecting extinction rates remain poorly understood. Mycoparasites of the genus Ampelomyces appear as good candidates for testing the role of a hyperparasite, i.e. a parasite of other parasites, in the regulation of their fungal hosts’ population dynamics. For this purpose, we first designed a quantitative PCR assay for detection of Ampelomyces spp. in field-collected samples. This newly developed molecular test was then applied to a large-scale sampling within the Åland archipelago, revealing that Ampelomyces is a widespread hyperparasite in this system, with high variability in prevalence among populations. We found that the hyperparasite was more common on leaves where multiple powdery mildew strains coexist, a pattern that may be attributed to differential exposure. Moreover, the prevalence of Ampelomyces at the plant level negatively affected the overwinter survival of its fungal host. We conclude that this hyperparasite may likely impact on its host population dynamics and argue for increased focus on the role of hyperparasites in disease dynamics.

Population level datasetThe excel file contains for each population: the name (Patch_ID), informations on the location (commune, village and geographic coordinates), the fraction of leaves bearing chamsothecia averaged over the analyzed plants (prop_chasmos), the powdery mildew abundance in July 2012 (PM_AA_july12), the total number of samples analyzed, the number of samples positive for Ampelomyces.Hyperparasite_patch_level_data.xlsxSample level datasetThe excel file contains for each sample: the name (Sample_ID), the population of origin (Patch), the plant name (Plant_Code), the fraction of leaves bearing chasmothecia (estimated at the plant level, Prop_chasmo_Plant), the presence/absence of multiple strains of powdery mildew within the sample (Mult_PM_strains) and the presence/absence of Ampelomyces based on the molecular detection test (Aq_PA)Hyperparasite_sample_level_data.xlsxQuadrat level datasetFor each quadrat, the excel sheet contains: the quadrat name (Quadrat_ID), population (Patch), the prevalence of Ampelomyces within the quadrat in autumn 2011 (Aq_prev), the proportion of plants found to be infected by the powdery mildew in july 2012 (Prop_PM_infect_plants_2012) and the proportion of leaves bearing chasmothecia in autumn 2011 (Prop_chasmos_2011)Hyperparasite_quadrat_level_dataset.xlsx