Plum tree pest, any ideas?

I have these on 2 of the plum trees in Bulgaria , only 2 of the trees though, the leaf looks swollen on the center vain at first , then swells to a large blob of mutated leaf looking like a cacoon the leaf cacoon is like a pea pod in texture it is very thicker than it should be

This is not something on the leaf this is the leaf, gets a red tinge in areas, chopped open for the first 2 weeks they had nothing inside visible at all..... then there are 1 or 2 tiny about 3mm long and 0.5mm wide very active bright orange almost flourescent caterpillers at one end that arch up and run off quickly

I cant find any description of these searching , they are like a sawfly or something, I have no photos of the orange beasties as they were rapidly squished due to speed, they dont seem to be leaf miners as they stay in the center vain....for now