on Phacelia, at least for pollen. Nectar is also used as flight fuel, as you suggest. Many pollen specialists, as Doug Yanega told me some years ago, will still use other plant species for nectar. The gathering of pollen and feeding on nectar are separate activities.

This female was only my second observation of pollen wasps. At the time I still thought, based on some early reading, that they used Penstemon. I've since learned, also by own observation, that almost all spp. of Pseudomasaris use Phacelia both for pollen and nectar.
You may prefer getting your gasoline at a certain station, but if you're out of gas you'll have to make do with what's nearby. At the time there was no Phacelia in the area.
I recommend reading "Plant-Pollinator Interactions" (2006, Waser & Ollerton, eds.; (1))

I don't think that Evans meant this categorically. One of the diagnostic characters of Masarinae (at least in North America) is a clavate (club-shaped) antenna. Those of males are just considerably bigger and more spectacular than the antennae of females. We have a couple of images of males on bugguide; for an example see here: 1 .
I don't have time to look it up right now, but I'm certain that a careful reading of H.E. Evans will yield the same results.

I was glad to see another Pseudomasaris, and to have a relatively 'cooperative' subject. Penstemon centranthifolius is beginning to bloom in the area, and I wonder whether I'll see these pollen wasps feeding in those flowers.

This insect may be caught up in the milkweed's pollinarium.... Great shot at any rate. Mike

in this case, it soon changed position.

I'm running out of adjectives to compliment your images with:-) Yes, you should see Pseudomasaris females gathering pollen from the Penstemon. Be on the lookout for males, too. They have bizarre, long, clubbed antennae.