It can be difficult to determine the culprit in cases like this because many insects chew foliage (including petals, sometimes preferentially) and leave the plant while they are not actively feeding. Plus, several feed at night so they are more hidden from predators. You can inspect the plants (once fresh flowers open, so the pests have something to eat again) after dark with a flashlight to see if you spot anything.

Potential culprits include an array of caterpillars (like those of the Camouflaged Looper, a native moth also named the Wavy-lined Emerald Moth), earwigs, young grasshoppers and katydids, and a wide array of beetles.

Insecticidal soap only impacts insects while wet and actively contacting the insect in question. Residues dried on the plant will have no effect on pests if they reappear later. Since these sprays have no residual, they can't be applied when the pests aren't apparent. We suggest stopping treatments until you/we can identify the culprit, which will then determine how to suppress them if needed. Otherwise, just clip off the damaged flower heads to promote faster rebloom (unless you're leaving seeds to ripen for birds) and monitor the plants for recurring damage. Not all pests are present all season long, so if only one generation occurs, the window of damage may already be closing (or will soon). Plus, as a near-native plant (native to the eastern half of the U.S. but not the mid-Atlantic), Coneflowers support good insect/wildlife diversity by providing them with food aside from just nectar, pollen, and seed, including many native insect species. In this regard, since overall plant health is not at risk from this type of damage, you may not need to take any further action.

Feel free to send us photos of any suspected chewers you'd like help identifying.

Miri