Hi, I'm not experienced with sawflies, but have you tried to strengthen your roses? You can bury old rusty nails (or other iron bits) near the main
root, and add powdered blood near the base of the plant. That seems to keep my roses happy for the most part. My main struggles with them are aphids, and black spot.Both are horrible in my area. I haven't got a great solution for either of those, but a
water hose at full blast for the aphids, and neem and pruning for the black spot. Good luck, and if I can find any other advice other than just to strengthen the plant from within, I will certainly share with you.