Weevil larva. Black vine weevil, taxus weevil, etc. All feed at night so they are rarely seen and leave the characteristic notches in the leaf edges.

Pretty much inevitable if you grow rhododendrons and there's not much that can be done about it other than keeping the plants in good condition through proper watering, mulching, etc. Nematodes, Tanglefoot and various chemical controls have thir advocates, but they will not be terribly effective in the long run. Rhododendrons with thinner leaves are far more prone to damage than those with thicker ones.

thank you! so far, these weevils don't seem to be affecting the plant in a detrimental way other than it just doesn't look very nice.

The larvae are in the soil, nibbling on the base of the trunk & the fine roots.

The adults are the ones that notch the leaves.