Hello,What food do you use for imago Aglais?
Are you just using fruit or something else?
Maybe fruit mousses?
Adult Aglais like flowers, such as Buddleja or Verbena. They will also take sugar water (50:50) or honey (50:50) on cotton wool. They can be a little difficult in a small space, they like to fly.
If you want them to lay eggs. I find that I do not put the nettle in too early. let them pair and allow the eggs to mature over a few days and then put the nettle in.
A good food I feed my forest butterflies (like admirals and tortiseshell) is banana and pineapple. They can be hard to feed, though.