Biological control of powdery mildew (PM) plant pathogens may offer a solution to traditional agro-chemical problems such as pesticide resistance, worker safety, pesticide residues and non-target effects. Mildew consumption by arthropod mycopredators is seldom studied and is therefore poorly understood. The coccinellid tribe Psylloborini is composed entirely of obligate consumers of various PM fungi and is represented in the western hemisphere by members of the genus Psyllobora Chevrolat. In western North America Psyllobora vigintimaculata Say is an obligate feeder of PM in natural and managed systems. The natural occurrence of this beetle has been documented in native and exotic landscape plants prone to PM over the course of one year through weekly presence-absence and density sampling. The insect was observed feeding on PM on 27 plant species in 14 different plant families. Positive correlations were found between the presence of PM in the landscape and the presence and number of P.vigintimaculata life stages on the afflicted plant. Additionally, positive correlations were observed between PM density and the presence and relative density of insects, suggesting an aggregative numerical response. Presence-sampling data indicates activity from late February through mid-December in Davis, California. The potential of P. vigintimaculata for biological control and management of PM is discussed.