From the image you sent it does not look like any pest is eating your Coneflower but it does look like the plant suffered from lack of water. The Coneflowers are tough and drought resistant but only after they have spent a year in the soil getting a deep root system established. If you just planted them 2 months ago and then a heat wave hit the poor plant just never got a root system growing so will need lots of water to save it.  Water every few days or when the top 2 inches of soil is dry to the touch. In the fall you can ignore the plant as it will go dormant when the cold weather arrives. I think the plant will survive the winter and resprout in the spring with fresh new growth.