In a travel I did to the southern parts of Pantanal in Brazil one month ago I came across vast plantations of maize. While driving in the middle of this corn-sea we had to stop several times to clean the windshield because the amount of Maize Hover Flies (Toxomerus politus) that got runned over was so great that we used several loads of water from the windshield cleaner to be able to see anything.
Also whenever we opened the windows or stopped somewhere, we would receive a visit of several of those flies that landed on us to probably lick our sweat or something. Some local people or tourists were even afraid of them thinking they were bees or wasps.
As soon as the maize plantations got scarce and were replaced by the local Cerrado, there was no more hover flies to be seen. So yeah, they are very connected to this plant, specially during this stage of the maize where it was flowering. This species looks common in eastern US too, so I guess people there might encounter them in this manner too.
I’ve seen other Toxomerus species in my garden and in more wild areas before, but never in such numbers. I wonder if the farmers know not to use chemicals during this stage since these flies do no harm and even help with the crops when their larva feed on aphids and such. Not to mention they fall prey to a number of other creatures too. Either way it felt like there was a lack of predators for these flies there.