My three pronged attack on greenfly :
1) Rub them into another dimension with finger and thumb
2a) Big tough shrubby plants can be hosed down with a strong jet of water
2b) Smaller plants can be tipped upside down and held under the tap to wash the
beasties of (put the pot in a tightly sealed plastic bag to keep the soil in
place)
3) Spray with a solution of water / washingup liquid / methelated spirits

Jenny