[metmom]

Mosquitoes are far older than the timeframe being discussed in the article. There are plenty of flying insects that have nothing to do with flowering plants, and preceded said plants by millions of years.

Since male mosquitoes eat nectar from plants, what did they eat before flowering plants appeared on the scene?

[RegulatorCountry]

Since male mosquitoes eat nectar from plants, what did they eat before flowering plants appeared on the scene?

They feted upon an unusually sweet substance emitted from primordial pond scum. It always goes back to pond scum.

[The_Victor]

Since male mosquitoes eat nectar from plants, what did they eat before flowering plants appeared on the scene?

They are called "extrafloral nectaries". Non-flowering plants produce nectar from the leaf petioles, mid-rib or leaf margin.

[ElectricStrawberry]

Both male AND female mosquitoes feed on “plant juices”, including nectar AND the photosynthate in phloem....and can quite easily pierce the skin of plants to the phloem to extract the photosynthate...especially soft-sided tropical plants.

As in, they are not nectar exclusivists like you want them to be....in any manner.....and even if they were today like you want them to be, that would not mean they were 300+ million years ago...it would mean that they are taking advantage of an easy food source.

Entomology is your friend.