Also-- what makes you think they are not aphids? They may not be, but I'm curious to know how you ruled this out.
Aphids are soft-bodied (and come in a lot of colors), so if you can smush them between your thumb and forefinger (with leaf in between), then my guess is they are aphids. If memory serves, I had an infestation on my shastas earlier this
spring and the aphids were black. In any case, you might try spraying an insecticidal soap (e.g., Safer Insect Soap) on them and see what happens. You can make your own soap-- see the thread on the main page for a couple of easy recipes.