This lovely beetle, whose full name is Coraliomela quadrimaculata, is a leaf-mining leaf beetle with a fondness for palms and coconut trees. It is found in South America, so we should give it its Spanish name, Barata-do-coqueiro. This is in fact the name given to several species of chrysomelid beetles, whose larvae feed on the young leaves of palm trees in Argentina and Brazil. The adults are fairly large (2.5 to 3.0 cm long) and feed on palm leaves, although the larvae seem to do the most damage. This particular species is a minor pest in the group and probably occurs widely without causing too much damage.
I came across these beetles on Yatai poñi or Yatay palms (Butia paraguayensis) whilst touring a ranch (San Juan Poriahu) in Corrientes Province, northeast Argentina. These small palms are a feature of the Ibara wetlands in this area where they are an important component of the grasslands.
The beetles were abundant in mid-March and could be seen mating on the palms in the late afternoon.
Many thanks to Ted MacRae [Beetles In The Bush] for identifying it for me.