Cibdela janthina is a sawfly of the family Argidae. This species originates from Sumatra in South-East Asia but had also been introduced to La Réunion in 2007 for biological pest control of Rubus alceifolius, a Rosaceae species that had become an invasive species.
It has a metallic dark-blue colour, the males have a length of approx. 8 mm and the females of 9.5 mm.
A parasitoid of C. janthina is Proterops borneoensis.