Diplotoxa messoria (Fallén, 1820)
Larvae in the stems. However, Nartshuk (2017a) and Nartshuk & Andersen (2012a) write that species would live in rotting stems, which might indicate that the species might be a saprophagous rather than a parasite!
Eleocharis palustris, quinqueflora.
distribution within Europe
Nartshuk (2012a, 2017a), Nartshuk & Andersen (2012a), Warrington & Perry (2020a).