10 foot tall holly bush leaves falling off
No sign of insects. The leaves on the very bottom look ok, but 95 percent have fallen off. No new growth detected. Should I cut it down?
Most probably, the cold weather hit your holly pretty hard. You're not the only one. Deep snow apparently protected the lower part of the bush. You can cut back branches that are dead, but otherwise, give it a chance to recover at its own pace. Here's an article on holly pruning: https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm