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There's a very easy way to tell H. trivittatus apart from all other Helophilus: it has a all-yellow face while the other species have a black vertical stripe. This black band is well visible in your 2nd small image above. H. trivittatus is a large species and the pale areas on the 4th tergite (3rd large plate on top of abdomen) usually form a band. Other species have elongated spots almost touching each other.

The spots on 4th tergite are H. hybridus board and darker than pale areas on previous tergites.

H. pendulus has narrower, sausage-shaped spots on 4th tergite.

See http://www.veluwe...hilus.html for photos of these species.

This leaves us with H. affinis to describe. It is not rare in Finland, but I understand it is nor often seen in Central Europe. The females of this species are close to H. pendulus, the males closer to H. hybridus.