Answer: Without knowing precisely which insect you're dealing with, it's hard to make a pesticide recommendation. Spotted cucumber beetles fit the description, but they're not generally pests of dahlias. Probably the best course of action for you is to capture a few of the critters and take them to your local Cooperative Extension office for positive i.d. The helpful folks there can make some recommendations for control. Phone (541) 672-4461.
In the meantime, hose the insects off your plants. Repeated hosing might discourage them enough to keep them permanently off your plants!
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