Holly and aphid

Hi again, one of the large shrubs (6ft tall) I had planted last year was a variegated holly (yellow and green) the new growth of which seemed to attract aphid. I thought this was because it was stressed because it was newly planted. This year however the aphid is already back! I have sprayed it as best I can but never thought of holly as a plant that would have a pest like this. Could anyone advise why aphid would be targeting this particular shrub.

Thanks

Ann