The two are awfully similar, but this just "looks" like L. helloides to me. Also, this is a bit south for L. dorcas I suspect (but I could be wrong). What plants they are associated with is often very helpful in telling them apart. L. dorcas feeds primarily on Shrubby cinquefoil - Dasiphora fruticosa (also called Potentilla fruticosa or floribunda), and it rarely strays far from it. I'm pretty sure it feeds on other related species in genus Potentilla too, since I've seen it associated with them too. It seems to love the nectar of its host plants best, and is most often seen perching or sitting on these plants and their flowers. L. helloides probably only feeds on Knotweeds (Polygonum), Docks Rumex, and a few related species, and while it stays close to these plants it seems to nectar more freely on other plants too. Generally L. helloides is from warmer places with longer summers, and that may affect it's habitat preferences too (more "southern" type habitats), while at it's southern limits I expect L. dorcas likes the habitats more like the north (cool acidic boggy places?). I don't know how much help that is.

Moved from ID Request.