Mycophagous ladybeetle (Psyllobora vigintiduopunctata) effectively suppressed powdery mildew on strawberry (Podosphaera aphanis), a cage trial in greenhouse

Abstract: Powdery mildew (PM) (Erysiphales), is a major fungal disease in many important
crops worldwide. Disease management of PM heavily relies on fungicides, which pose risks to
environmental and human health. However, effective biological control options for PM remain limited. Mycophagous ladybeetles represent an unexplored group of macro-biocontrol agents with potential to control PM. Psyllobora vigintiduopunctata (P22), an obligate feeder of PM, consumes fungal spores and mycelium during both larval and adult stages. In this study, we evaluated the efficacy of P22 against strawberry PM in cages under greenhouse conditions over a nine-week period in curative and preventative settings. We assessed the effects of release density (one vs. two couples per release) and supplementary food (bee pollen and 20 % sugar water) on beetle population dynamics and disease suppression. PM suppression provided by P22 were compared with an untreated treatment and a fungicide spray program, and the compatibility of P22 with spraying was also examined. In the curative trial, a single release of either one or two couples significantly suppressed PM compared with the untreated treatment and also achieved efficacy comparable to the spray treatment. In the preventative trial, one couple was sufficient to prevent disease outbreak. Notably, during the final two weeks of the curative trial, PM was completely eliminated in treatments with P22 only, whereas disease symptoms persisted under the spray treatment and combination treatment. Beetle population dynamics, shown in curative trial, were strongly dependent on PM availability, while supplementary food enhanced larval survival and number of adults when PM was absent. Furthermore, spraying affected larval survival and reduced PM availability, resulting in high larval mortality in combination treatment. These findings demonstrated the potential of P22 as a sustainable biological control agent for strawberry PM, and further assessment at bigger scales is warranted.