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. Published by Plantsman Publishing, it is available for about $25 through the Illinois Arborist Association in Downers Grove; call (630) 960-5922. 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.
Birch leafminer: Look for small mines when blooming starts.
Pine needle scale: Red crawlers are active when blooming starts.
Taxus mealybug: Nymphs are active during blooming.
Lilac/ash borer: Egg hatch begins in full to late bloom.
Oystershell scale (brown race): Crawlers hatch and are active in full to late bloom.
Oystershell scale (gray race): Crawlers hatch when blooming finishes.
Black vine weevil: Look for feeding notches as blooming finishes.
Bronze birch borer: Egg hatch begins when blooming finishes.
Elm leaf beetle: Feeding damage begins when blooming finishes.