I have had healthy stonecrop for 5 years and then this year one of the plants started turning black and watery. I cut that plant down to the ground and removed some of the soil around it. Now I have a pest eating the other two plants. There are both round holes in some leaves and other leaves are being chewed from the outside of the leaves, leaving jagged remains. I have searched but cannot find the insect. Does anyone have any ideas and if so, is there a treatment to rid the plants of these hungry pests? See photo attached. Thanks!