Oleander aphid

My Hoya carnosa is heavily infested by aphids of the Aphis nerii species. Bright yellow, 2 mm long drinking sap using their rostrum.
In case of threat they secret a yellow secretion containing molecules toxic for birds and spiders.
But they can be eaten by the larvae of some hoverflies (Syrphid flies). In the third picture you see a larva lifting an aphid from the leaf. In the second picture you can see the yellow toxic droplets the aphid tries to use to defend itself but they are useless against the larva.
The day after, larva was thicker and had moved to another leaf.