Downesia sulcata is a species of beetle of the family Chrysomelidae. It is found in Thailand and Vietnam.
Adults reach a length of about 5.5 mm. This species is similar to Downesia tarsata. The adults are reddish-yellow. There are three raised ribs on each elytron, separated from each other by two rows of deeply depressed dots. Furthermore, the posterior third of the elytra is black.
No host plant has been documented for this species.
Some sources list the author as Raffaello Gestro, but this is in error.