Thank you for contacting the UVM Master Gardener Helpline with your question. Your photographs were very helpful.

Ann, the Director of the Plant Diagnostic Clinic, confirmed your suspicion that you have a sawfly. She recommended that you try an insecticidal soap or neem. She is not sure that diatomaceous earth would do anything.

We offer a few links that you might find helpful:

University of Maryland publication entitled “Sawflies”: https://extension.umd.edu/resource/sawflies/

University of Minnesota Extension: publication entitled “Sawflies”: https://extension.umn.edu/yard-and-garden-insects/sawflies

North Carolina State Extension publication entitled “Hibiscus Sawfly”: https://content.ces.ncsu.edu/hibiscus-sawfly

Finally, the Pacific Northwest Extension Pest Management Handbooks site has an article entitled “Landscape pests-Sawfly”: https://pnwhandbooks.org/insect/hort/landscape/common/landscape-sawfly

We hope this information is helpful. If you have any additional questions, please feel free to reach out.