Personally I'd simply give the white fly a good blast from the hose and ignore the little black insects on the nasturtium leaves. Only use washing up liquid if yours is one of the eco friendly ones like Ecover.

I don't ignore the black fly on Nasturtium as I grow them for eating. The easiest way to get rid of them is to pinch off all the affected leaves and discard them.

Thank you, Bo Bangles x