Frass on Quince

I noticed lots of insect frass on the calyces of a couple of quince this year. Quince are famous for having few pests or diseases, so I was a bit annoyed to find this as well as quite a lot of scab. However, on close inspection the damage is mainly on the exterior, extending only a little way into the fruit at the calyx end.

I'm not sure what did the damage, I couldn't find anything among the frass or inside, but I think whatever it was, it's an opportunist bug of some kind rather than a serious specific pest of quince. I'll need to keep an eye out for it, as even this small amount of external damage will rapidly turn to brown rot in store.