If you have used a systemic insecticide the aphids will die as they feed so death might not be immediate so perhaps leave them alone now. I would give the pants a feed with something like Vitax Q4.

I'd also feed and water well to encourage new growth.

Sorry, should have said catapillars not aphids.

Thank you both very much - I’ll water and feed - and I’m glad to hear the spray may take a while to work- I was a bit disheartened that there were lots left this morning !