text: If you are in the USA.  I recommend that you call your local County Cooperative Extension Service office.  They can help you identify your pest.\n\nHere are two websites with many excellent images.\n\nI don't know much about insects, but I was researching Sawflies earlier this year, and I believe some of them pupate inside of stems.\n\nWhatever it is, I would first try to find out what it is.  It may have an important role elsewhere in your garden.\n\nWhen you discover what it is, if you decide to control it, please do so with a soap spray.  Chances are birds are visiting your garden, and you wouldn't want them feeding on toxic insects.  Also, many products on the market are hazardous to YOUR health, and stay in the environment for a long time.\n\nIf you are observant, you learn much important and interesting information about insects.  Examine nearby plants,  does it feed on other plants, or is it selective.  What time of year does it appear and disappear.\nWhere is it on the plant?  On the leaves, stems, etc.\n\nGood luck, and enjoy your garden.  Black Knight is one of my favorite Buddelias.