I find the culprit is normally a catterpillar/maggot, they have been cropping up the last few years, tiny little green threads, they hide well by sticking two leaves together, or folding the edge of a leaf over, they eventually spin a cocoon if not caught sooner.
I have no idea what they are, but this year the same critters have been atatcking my blueberries and tomatoes, with these they even eat into the fruits, they don't seem to stay inside, just eat a hole in one side and out the other.
They are very small, only 4mm long by 1mm wide, and pale green. Their leaf sticking antics are often very covert, such as sticking a leaf to one above it, so when looking down they appear just to be overlapping fairly normally.
I have squished about five this year, they never seem to reach particularly damaging levels, just nibbble holes in leaves, damage a few fruit and then disappear.
