could they have been caugt by the late frosts?

This is probably Pear Midge. If you split a pearlet when it is first affected it has tiny white grubs at its centre. The pear usually tips a little to one side before it goes black. If the tree is on limiting growth root stock, try snipping pears off when they tilt and discolour, and crust them underfoot. For next year, try keeping the ground below well howed. Spray with Bifenthrin at white bud, or pick them over early and exterminate.

thanks - very helpful.