According to different internet sources The Horned Sungem (Heliactin bilophus) is reported to have the fastest wingbeat per second in hummingbirds during hovering. It can make 90 wingbeats per second when it's hovering to drink nectar from flowers.
https://simple.wikipedia.org/wiki/Horned_Sungem
http://worldbirds.eu/abch/horned_sungem.htm
http://www.gopetsamerica.com/animals/bird_records.aspx
However, I haven't found the source for this information. Does anyone know the source (article, report or book)?
Regards,
Ronny