Thanks for the question.

While the picture lacks good resolution, I believe that they are milkweed stem weevils (Rhyssomatus lineaticollis). Adults initially feed on the top milkweed leaves. This is what you are now observing. After a period of time and feeding on plant juices, female weevils move to the lower parts of the stem and chew several sequential holes in the stem. Females then lay a single egg per hole and larvae complete development inside the stem while feeding on plant tissue. All of this activity is not good for the milkweed and often the stem bends and the top of the plant wilts and falls over. This is usually fatal to the plant.  While spraying a pesticide on your milkweed would take care of the weevils, such a pesticide might also be fatal to monarchs so you would not be gaining much. The most effective way to deal with them, though labor intensive, is to physically remove them from the milkweed and put them in a container of soapy water. If there is extensive damage to several plants, monarchs will simply look elsewhere to feed. This species of weevil strongly prefers swamp milkweed so I’m assuming that is the type of milkweed you have. You may want to consider planting a different variety of milkweed to prevent this problem from recurring?  Here are some sites that will provide you further information on these and other points:

https://bugguide.net/node/view/1375554

http://minnesotaseasons.com/Insects/milkweed_stem_weevil.html - :~:text=Milkweed stem weevil is a small snout beetle.&text=Adults feed on the leaves,5.5 to 6.5 mm) long.

http://hyg.ipm.illinois.edu/article.php?id=693 - :~:text=They feed on the midvein,to wilt and break off.&text=Milkweed weevil adult stem feeding damage.

http://hyg.ipm.illinois.edu/article.php?id=693 - :~:text=Rhyssomatus lineaticollis is commonly referred,almost one-quarter inch long.&text=Adults emerge in May and,meadii, a federally threatened species.

Good Luck.

Glad to have been able to help you.  Good luck with your milkweed.