Thanks for the question.

Image #4921 is the larval stage of the multicolored Asian ladybeetle (Harmonoaaxyridis axyridis).

Images #4924 and #4922 are the same. They show the pupal stage of a multicolored Asian ladybeetle (Harmonoaaxyridis axyridis). Outwardly, the pupal and adult stages have some similarities. There are three striking differences. The pupal stage remains firmly attached to the plum leaf and cannot fly. This is why you couldn’t knock them off with your hose. It is not laying eggs on the leaf.   Secondly in the pupal state, some body segmentation is still visible. Thirdly, the markings on the pupae are different from adult markings. I think that this is probably why you didn’t think they were Asian beetles.

See (the first site shows the pupal stage; the second site shows the larval stage):

https://bugguide.net/node/view/1653009

https://bugguide.net/node/view/1593345

https://extension.umn.edu/nuisance-insects/multicolored-asian-lady-beetles

https://www.ars.usda.gov/oc/br/lbeetle/index/

As you probably know, these beetles are common in Minnesota and are found on plum trees when the fruit is damaged or ripe. They generally are considered beneficial insects and rarely become a nuisance. Sometimes in the fall when plums are ripe, these beetles may congregate on the fruit at which time the appeal of the fruit might be diminished.  I seriously doubt that they are eating the plum leaves.  Their favorite food on plum trees is aphids. If you are seeing abnormal foliage shapes on your plums, this is most likely due to aphids. These aphids can cause leaf curling, stunted growth, and reduced fruit production. In past seasons did you ever notice any aphids on your plums? Any presence of honey dew? See:

https://ipm.ucanr.edu/agriculture/plum/leaf-curl-plum-aphid/ - gsc.tab=0

https://www.gardeningknowhow.com/edible/fruits/plum/control-leaf-curl-plum-aphids.htm

Good luck. Please get back to us with any additional, related questions.