This is another small Belvosia-type tachinid from Peru – compare this with my photos of a similar taxon from French Guiana. This is much more heavily dusted than other, larger Belvosia spp. but the final tergite is white-dusted like the others.
EDIT (25/2/2010): Norm Woodley today got in touch and has said that these species with more dusting used to be placed in the genus Triachora but Monty Wood has recently synonymized it with Belvosia.
EDIT (17/10/2010): On closer examination I make this Atacta sp. but this is a bit of a complex group so I would prefer confirmation.