Answer: What you describe sounds like feeding by pear slugs. Cherry tree pear slugs are the larvae of the black-and-yellow sawflies which are predators of stone fruit trees and some ornamentals. Adult sawflies appear in the late spring at which time the females lay their clusters of eggs on the leaves of the cherry tree. Within a matter of weeks the larvae hatch from the eggs on the cherry tree leaves and begin to feed on the foliage. The cherry tree pear slugs emit a slimy, olive green substance which gives them the appearance of shiny, slugs. It is this material that the larvae exude which makes some of them appear dark green rather than the more common orange. The amount exuded can affect coloring because of its adherance to the larval body. Cherry tree pear slugs feed on the leaf foliage for approximately one month?s time at which point the pear slugs drop to the ground and burrow into the soil. The cherry tree pear slugs then pupate in the soil and later emerge as adult black-and-yellow sawflies to begin the reproducing and feeding cycle again. They also feed on rose leaves.
The best control is Insecticidal Soap when the larvae are actively feeding. Now that the pests are pupating in the soil, you can cultivate the soil around the affected plants to expose the pests to the elements and to hungry birds. Carefully inspect your plants next spring and summer and either hand pick the larvae or use Insecticidal Soap.
Best wishes with your garden!
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