Damage to nectarines

I have a nectarine in a polytunnel. The first year it had a good crop but since then something is destroying nearly every fruit before it has a chance to ripen and it is at it again this year. There are flies about but no wasps (bit early yet), also ants. Has anyone any suggestions of what to look for? Could it be ants, insects, flies or slugs/snails? Last year I wrapped fleece round some of the branches but the fruit was still spoiled.

I found these today.

 

Looks a bit like some kind of grub or moth Caterpillar.
Have you cut one open?

 

No grubs inside. During a night visit I saw slugs on the polythene and an earwig on a nectarine. So could ne a mixture of the 2.

 

Yeah, I think earwigs could be the culprit.