Hi Tardis
I think you'll find some sort of bug is to blame even if you can't see them now. Something like greenfly or thrips or red spider mite damage the very young foliage so that as it grows it distorts. Nothing you can do if you want the leaves safe for consumption by caterpillars except washing with a strong spray of water on a regular basis to dislodge pests before they can get a strong hold.
The Monarch butterfly caterpillar in the top left of the attached photo is about 3 days old and just over 1cm long. After about 10 - 12 days, they grow to the size of the one in the bottom of the photo. It took ages to get two unpredictable caterpillars in close proximity!
It’s been another busy couple of weeks. About 12 caterpillars have now transformed into chrysalises. Yet again, we’ve had to cull eggs and caterpillars. Probably getting on for 300.
We’ve tried to make some of our milkweed a no go area for caterpillars, so hopefully there will be some flowers in bloom for new butterflies in a week or two's time.
Has anyone tried to breed ladybirds to keep aphids at bay?