Honeylocust plant bugs are truly a here-today-gone-tomorrow kind of pest. They emerge in May to feed exclusively on the new growth of honeylocusts and are gone by mid- to late-June. These light-green bugs are about three-eighths of an inch long and are highly active. Shaking a branch over a sheet of paper easily reveals their presence.
Honeylocust plant bugs suck plant juices, producing scattered brown spots and distorted growth. Young leaves can be killed. Unless infestations are severe, trees can tolerate some damage. A significant plant bug population is generally considered to be six or more insects shaken from six to eight inches of new growth on a branch. In these cases, twig ends will appear visibly damaged and insecticide treatments should be considered.
Any spraying should be done when insects are small. Mature bugs in the last stages of an infestation in June are hard to kill and will disappear shortly anyway. Most shade-tree contact insecticides and insecticidal soaps are effective.
For more information, see the following Colorado State University Extension fact sheet(s).