Looking at the taxonomic level of insect families, Labandeira and Sepkoski could find no evidence for any positive impact of the angiosperm radiation upon insect diversity. The insect radiation began in the early Carboniferous, some 325 million years ago, got derailed once in the greatest of all mass extinctions at the end of the Permian (when eight of twenty-seven insect orders died), began again in the subsequent Triassic period, and has never stopped since. In fact, and if anything, increase in number of families actually seems to have dropped somewhat during the Cretaceous, as the angiosperms flowered!
Dinosaur in a Haystack, p 100.