The insects are the aptly-named Yucca Plant Bug. The linked article provides life cycle information and some management options if you decide to use insecticide to control them. (Otherwise, a strong spray of plain water from a garden hose should remove many of them, at least for the short term.) With about three generations per year, any management tactic may need to be repeated later in the summer. Be aware that if you decide to use a neonicotinoid-class insecticide, you'll need to hire a certified pesticide applicator to buy and apply it legally in Maryland. Many landscapers and arborists have this license.

Leaf damage is permanent, so any leaves stippled and discolored by their feeding won't green-up again, but as they are covered-up by new growth and naturally shed by the plant, the Yucca will gradually look better on its own. You should not need to do anything special to boost the Yucca's health, although alleviating drought stress by watering it periodically (even given the good drought tolerance Yucca has) should help it from developing other stress symptoms during this ongoing drought.

Miri