The insect is a whitefly, in the family Aleyrodidae.
Here in western Oregon, whiteflies tend to specialize on declining annuals and perennials late in the season. At this time of year, whiteflies have little significance because the plants are either normally declining (annuals) or are getting ready to shed their leaves (deciduous perennials).
Periodic harsh water sprays can effectively discourage large populations. Or one may use direct hits of commercial insecticidal soap spray to kill the adults and youngsters. Don't use a homemade soapy concoction as that may damage the plant worse than the pests.
Thank you very much. This is very helpful information.
You're welcome, Bob.