Answer: Little flies won't hurt the rose buds but I suspect what you are seeing are black aphids. Aphids will suck the fluids from the tissues of leaves and flower buds so you don't want them hanging around your garden. To test whether the insects are flies or aphids, sharply tap the top of the rose bud; flies will fly away and aphids will just keep on feeding. If you're dealing with aphids, Insecticidal Soap will control the population and it's safe to use around people and pets. It contains fatty acids of selected plants and will degrade in a few hours. Roses can be sensitive to the fatty acids, though, so spray in the morning or at dusk but not during a hot sunny afternoon. Several spray applications may be needed and be sure to coat the undersides of the leaves as well as the rose buds.
Best wishes with your new roses!
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