What created this cocoon on a beach plum?

February 27, 2024 Ask the Expert, Fruit Trees and Small Fruits, Managing Insect, Diseases, and Animal Pests

Question:

I recently discovered this growth/cocoon on a young beach plum. It is only about 5/8″ long and at first assumed it to be some kind of cocoon given the perfectly round opening, only it appears to the be the same woody material as growing on the beach plum (or perhaps very well camouflaged). Any thoughts on what might have created or caused this?

branch

Answer:

Jonathan Foster, Home Horticulture Outreach Professional

I reached out to our staff entomologist, Charlie Armstrong, and will provide his response:

“Yes, I think it’s an empty sawfly cocoon. It looks very much to me like the ones I find on our house and garage, from the Introduced Pine Sawfly. I’m 99% sure that’s what that is. Maybe not that same species, but definitely a sawfly I would say. Here are a few great examples (and the ‘end’ always pops off or opens up cleanly like that after they emerge):

They are not really anything to worry about unless you end up with an outbreak of sawfly larvae, on whatever plant they are living on, then that’s obviously not a good thing. But finding the empty cocoons of adult sawflies is definitely not anything to worry about, as there will always be some adult sawflies around in the environment.”