Answer: What you describe sounds like damage from the geranium bud worm. The culprit is a moth which lays eggs on the outsides of the flower buds. The eggs hatch into little larvae which burrow into the unopened bud and feed on the flower. Then they work their way out of the empty flower bud, drop to the soil to pupate and then fly away as moths. In addition to the hollow flower buds, look for small bore holes in unopened buds and black frass (droppings) on the leaves. If you find these, I'll bet that's the problem. It's difficult to kill the larvae once they've enter the flower buds so you'll need to concentrate on killing the moths. Orthene sprayed according to label directions should help.
Best wishes with your geraniums!
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