The harlequin ladybird, Harmonia axyridis (Coleoptera, Coccinellidae), is one of the worst invasive species in Europe. Originally from eastern Asia, it was introduced as biocontrol in North America, it has since spread over the rest of the world and has a negative effect on native insects as well as food production and human health. The ectoparasitic fungus Hesperomyces harmoniae nom. prov. (Ascomycota, Laboulbeniomycetes, Laboulbeniales) is found on Ha. axyridis worldwide. In laboratory settings infection of He. harmoniae affect Ha. axyridis mortality. However, much is still unclear about the spread and effects of He. harmoniae on Ha. axyridis. This project (1) explores the factors that determine He. harmoniae infections of Ha. axyridis through data analysis from experiments the lab, in the field, and gathered from citizen science. It (2) investigates the population genetics to determine how He. harmoniae has spread globally through DNA sequencing and statistical analysis. Lastly, the project (3) looks at the efficacy of He. harmoniae as a biocontrol agent through laboratory experiments and data from the field. It is necessary to create a greater understanding of how natural enemies infect, spread, and control the invasive alien Ha. axyridis, and the ubiquitous He. harmoniae makes a great target for investigation in this regard.