Species of Macrosiagon Hentz are known to be wasp and bee parasitoids. Here, we present information on Macrosiagon octomaculata (Gerstaecker, 1855), including eggs and triungulinids, found on Paepalanthus polyanthus (Bong.) Sano (Eriocaulaceae) blooming in restinga habitat on Santa Catarina Island, South Brazil. This is the first record of an Eriocaulaceae species playing an important role in the Macrosiagon bi...