Looks like you have an insect problem we affectionately call pear slug. It is really the pear sawfly but the larvae sure look like a little slug - if you find it. It just skeletonizes the leaf as we see in your images. You can read more about it here (and on many other crops): https://pnwhandbooks.org/insect/tree-fruit/pear/pear-pear-sawfly-pear-slug

Hi Mark, if you click on the link Jay sent you, the pesticide options for you are detailed. These insects have a second generation later in the summer, you are likely to see another round in August or so. The link has your chemical options as well. If you can catch this generation before they strat to drop to the ground to pupate, you can drastically reduce the number available to eat the leaves later this season. If not, a treatment when you start seeing the next generation is helpful. You want to catch them while still in the tree, as there's no treatment for them once they drop to the ground to pupate. The damage can be drastic on small/ young trees, but mature trees can often stand a minor infestation with little overall damage to the tree. I hope this helps, Nicole