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My mistake :@ - I misread the caption in Shorrocks (Invertebrate Types: Drosophila p.36). I should have said Drosophila immigrans, not funebris. This is a fruit-feeding species, so perhaps the larva fell from a rotting fruit, or was stuck on a bird's beak and was wiped off on the leaf.
The pupal horns are for breathing when the puparium is in deep liquid. The hairs at the tip of the tubes keep the opening at the surface of the liquid, so the whole puparium can be submerged, but continues to breathe.