Many insect events correlate with the blooming of Vanhoutte spirea, Spiraea x vanhouttei, which is occurring in central Illinois. The book Coincide by Don Orton covers this topic very well and was written primarily from data collected in Illinois. It can also be ordered through bookstores. Any company responsible for insect control on trees and shrubs should have this book. The following information from Coincide should help practitioners plan scouting activities.
Nymphs are active during blooming.
Crawlers hatch when blooming finishes.