The coccinellid tribe Psylloborini (Halyziini) is entirely comprised of obligate consumers of powdery mildew (PM) fungi (Ascomycota: Erysiphales). The small ashy gray ladybird beetle, Psyllobora vigintimaculata Say, a North American species, is being evaluated for use as a biological control agent against PM in greenhouse systems. Individual larvae were reared on PM-infected leaf discs in a laboratory incubator to quantify the removal of PM due to this insect’s feeding. The leaf area cleaned and the background growth of PM were measured with image analysis software using periodic digital images. Leaf discs exposed to neonate larvae for 192 hours showed a significant decrease in PM growth as compared to an untreated control, and leaf discs exposed to 3rd instar larvae for 96 hours showed a significant decrease in infected leaf area. A simple model based on these data predicts that an individual larva cleans 6.3±3.3cm² leaf area of all visible PM hyphae and conidia from the time of egg eclosion until successful pupation. This quantification of the consumption abilities of P. vigintimaculata is essential to its evaluation for use as an effective biological control agent or as a biological tactic within an integrated disease management program against PM fungi.