Lily damage from larvae

[Nickz]

Hi,
Here's what i've been finding on my lily leaves:

I only find them on top of the leaves, never below. However after manually removing them i found others the day after, letting me think they might hatch from below.
My question is, is there a way to prevent this next time? There are fish in the pond.

Has anyone had experience with bacillus thuringiensis treatments in ponds? Would it have worked in my case?

Thanks

 

[Nickz]

Even this year i'm starting to have the same issue. This time i think i've found their eggs and removed them:

However the leaf already has some damage even if i could not find any larvae yet. Maybe adults also do the same kind of damage. The suspect:

 

[Nickz]

Just had a look at my old photos in my first post and i could spot some of the same eggs i didn't notice last year. I think i'm on the right track.