Relationships between the Pathogen , the Phytophagous Mite (Acari: Tetranychidae) and the Predatory Mite (Acari: Phytoseiidae) in Oak.

Food webs on forest trees include plant pathogens, arthropods, and their natural enemies. To increase the understanding of the impact of a plant pathogen on herbivore-natural enemy interactions, we studied the powdery mildew fungus , the phytophagous mite , and the predatory and mycophagous mite in pedunculate oak () leaves. In June, July and August of 2016, we assessed the severity of powdery mildew, mite population density and adult female mite size in 30 trees in three forests near Belgrade, Serbia. In August, the infection severity of related positively to the population density of and negatively to the body size of females. Throughout the vegetative season, the infection severity of related positively to the population density of but not to its body size. The effect of on the population density and adult size of was not mediated by the population density of , and . Interactions were consistent in all forests and varied with the summer month. Our findings indicate that can influence the average body size and population densities of prey and predatory mites studied, irrespective of predator-prey relationships.