This is a Cottony Cushion Scale, Icerya purchasi. The aphid-like creatures are probably young individuals, known as "crawlers". The females attach themselves and grow the white, fluted egg sack.

This species almost wiped out the citrus industry because they're non-native and have no real native predators. It was only with the introduction of a species of ladybug that eats them that they were brought under control- one of the first successful uses of biological control.