I haven't tried the sunflower oil spray, but manual removal and extermination of the red adults and their unpleasant larvae is effective, though you have to be vigilant. And I would recommend using gloves to deal with the larvae which cover themselves with their own excrement. The adults tend to do a backwards flip when the plant is disturbed, landing on their backs and exposing their black bellies, which makes them difficult to see. Some people suggest putting a sheet of White paper under the plant so the bugs remain visible. Don't forget to check other vulnerable plants like fritillaries.