Thank you for your inquiry. This is a type of "Stink Bug".  They lay their eggs on the leaves, reproduce quickly, and are quite destructive (not to mention rather appalling in appearance and in sheer numbers).   My garden has just recovered from an infestation of these as well. Many other Colorado gardeners have had them this year.  Unfortunately some trees attract them and locust is one of them

There are several options for eradication of these pests. I opted for repeated applications of a Pyrethrin spray, followed by applications of Diatomaceous Earth.

Another choice is Neem Oil spray. There are more organic sprays such as insecticidal soaps but, they are not as effective on hard shelled insects. They can be sprayed with a 50/50 soap and water mixture, but there again, not as effective as chemical eradication.  

Because you are dealing with a tree there are some special challenges. I will include some links here for information on trapping and other methods that are possible options:

http://ipm.ucanr.edu/PMG/PESTNOTES/pn74169.html

https://extension.psu.edu/brown-marmorated-stink-bug

Please do not hesitate to contact us with any further questions and best wishes for a swift and thorough removal.

Thank You,
Traci