Thanks for your question.

I believe these are insect holes in the bark but in the absence of pictures of the actual insect, I can only provide you with a reasonable guess as to the type. I would expect that you may have seen woodpeckers attacking your locust going after the insects under the bark.

The insect involved is a locust borer (a type of beetle). There are two different species: a honey locust borer (Agrilus difficilis) and a black locust borer (Robinia pseudoacacia). If you know for sure that your locust is a honey locust, then the borer is the first of these. If perhaps you have a black locust, then the borer is the second of these.

The life cycles of both are quite similar. Adults lay eggs in late summer in the locust bark. These eggs quickly hatch into larvae that bore through the bark.  I suspect you are now looking at these holes. It would have been easy not to have seen them last summer. These holes now appear (mid-April 2024) to be missing pieces of bark. I suspect this reflects woodpeckers trying to get at these larvae. These larvae overwintered in the tree and will eventually emerge as adults in late summer of 2024. Then the fun begins all over again. It is also possible that these holes in the bark were made by adult borers emerging from the tree in late summer 2023. See the following for further information on these and related points:

https://www.uky.edu/Ag/Entomology/treepestguide/honeylocust.html

https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ENTO-141/ENTO-423.pdf

https://extension.usu.edu/pests/ipm/ornamental-pest-guide/arthopods/wood-borers/honeylocust-borer

https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/honeylocust/branchesholes.html

Sometimes borer infestations indicate a tree that was previously stressed. Perhaps the droughts of the 2022 and 2023 seasons led to some stress in your locust? Regardless of whether the severity of the borer infestation and/or the overall condition of your tree are significant issues, we would strongly suggest that you have a licensed, professional arborist make an on-site assessment and recommendation. Insecticides exist to deal with this insect, but their application is not really a DIY undertaking. See the following for guidelines regarding the identification of such an individual:

https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

Good luck and thank you for consulting us.



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Glad to be of assistance.

Remember that you need to break the cycle of this borer.  Ideally this means to eliminate as many of the larvae as possible.  Once adult beetles are present, they will start laying eggs for the 2025 brood.  These eggs will probably be resistant to insecticides.  If you decide, after assessment by an arborist, to remove the tree, all debris should be removed from your yard.

Good Luck.



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One final point.  Locusts are also very susceptible to scale.  In short, should you remove the locust I would urge you to replace it with something else.  

See the following for some possibilities:

https://www.dnr.state.mn.us/treecare/righttree-shrub.html - :~:text=Elms, maples, oaks, walnut,windbreaks, fiber, and biomass.

https://extension.umn.edu/trees-and-shrubs/trees-and-shrubs-minnesota-landscapes

Good luck