Hi Phyl,
It sounds like you have some type of Stem Borer. The best thing to do is cut down all the stalks, make sure you get all of them picked up, and dispose of them in the garbage or burn them if you can.
I just did a little search and found one called a Stalk Borer that seem to like Rudbeckia. It might be the one you have. Here's the info:

Stalk borer, Papaipema nebris.
This insect is a borer in aster. This borer infests an occasional stalk of many kinds of herbaceous plants and it frequently causes rather severe injury to dahlia. As a rule its presence escapes notice until the plant begins to wilt. Then it is too late for the plant to recover. The larva tunnels up and down inside the stem, and the top portion usually wilts and later dies. There is one annual generation. The moths emerge in September and October and lay eggs on the stalks of their food plants, in which stage the insect passes the winter. The eggs hatch in May or early June. The young larva begins to feed on the leaves of the nearest food plant, and later tunnels in the stem. The mature larva is nearly 1 ½" long, grayish brown with one white dorsal stripe and two white lateral stripes on each side. On the front half of the body the lateral stripes are interrupted, and the lower brown stripe extends forward onto the side of the head.

Burning all the old stalks, if allowed, and destroying weeds at the edges of the garden helps control this insect. When needed, methoxychlor, which is among the compounds registered for use against this pest in Connecticut, applied as a dust, in June, should control this pest. Consult the label for dosage rates and safety precautions.

Hope that helps,
Remy

remy, how generous of you to take the time to look up that info! ~~ a *stalk borer* certainly sounds right on ~~ probably a different one tho ~~ these weren't even 1/2" long; & white with a black head ~~

your help was appreciated; thank you ~ phyl

p.s. forgot to ask ~~ do any of you use something systemic for stalk borers? when? thanks again, phyl