There have been tiny insects on one of my spirea bushes for the last two summers. The leaves are thinning out and the plant just looks generally "tired". I would like to save it, if possible, without using harsh chemicals. There are what appear to be tiny nests within individual flower clusters. There are also small bumps along the branches, which may have nothing to do with the problem - I haven't looked this closely before. When they hatch, there are thousands of these insects, which I cannot describe, as they are so small they look to me like tiny dots moving up and down the branches. The leaves do not appear to be chewed, but rather wilted. I am wondering if this could be a sap-sucking insect. I soaked the entire plant with Trounce last year, after I noticed the insects, without much luck. Is there help for this plant?
