Answer: There are a number of pests that are fond of vegetable plants in general and tomatoes in particular. What you've described sounds like a cucumber beetle or vegetable weevil. Since they are congregated on the vine, look to see if they're feeding on other insects, like aphids, or if they're actually feeding on plant material. Their behavior will indicate whether they're beneficial or destructive. I'm partial to "when in doubt, find out", but I suspect that the insects are not on the list of "good guys" in the garden.
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