Sawfly Caliroa Cerasi

Hi all. I have a problem with the larvae of this sawfly on my Hawthorn, and Amelanchier canadensis leaves. Both are looking skeletonized. I see that there are no natural predators and i don't really want to use pesticides. Do you think hand picking them off and putting in salted water would kill them? I can foresee a bigger problem next year if I don't get rid of them as they will pupate and overwinter in the soil. Thanks all.