http://www.sciencemag.org/news/2019/11/amber-encased-beetle-may-have-been-one-first-insects-pollinate-flowers

An ancient beetle that nibbled a flower and got trapped in amber for nearly 100 million years has become the earliest direct evidence of insects pollinating flowering plants, researchers report today.

Scientists have long thought that insect pollination was key to the rapid spread of flowers during the Cretaceous period, about 145 million to 66 million years ago. But they’ve lacked solid evidence.