The male (right) and female (left) here were two of many Apolysis that were visiting the flowers of Ivesia santolinoides (Rosaceae) in the alpine fell-fields at ~8800' atop Mt. Pinos.

Beyond the small size and general gestalt here, some of the characters pointing to Apolysis are the: long proboscis; blunt antennae; three posterior cells; and absence of a discal cell (i.e. the cross-vein m-cu that usually "closes" the discal cell at it's distal end is lacking).

The photos here illustrate something I read in the 2nd paragraph of the interesting & informative introduction to the World Catalog of Bee Flies (Diptera: Bombyliidae) Web Site, quoted below (with italic emphasis mine):

"Adult bee flies are nectar feeders and females are obligate pollen feeders, obtaining pollen from anthophilous plants as a necessary requirement for the nourishment of developing ova."
I guess the pollen provides protein for the females that's lacking in the sugary nectar alone. I've often seen bee flies nimbly nibbling at pollen in anthers, far from the nectaries usually located near the base of a corolla. Now I understand the situation a bit better. The photos in this series illustrate the female here probing the anthers for pollen, and afterwards (in the last two photos) diving head first towards the nectaries at the base of the corrola to take some nectar as well.