The article presents data on the detection of mould fungi in the system of Aesculus hippocastanum – Cameraria ohridella which is an invasive pest of chestnuts. Entomological and mycological studies were conducted using standard methods . The study determined the species composition, occurrence index and quantitative indicators of the micromycetes present in the leaf tissues of Aesculus hippocastanum and Cameraria ohridella caterpillars.
