to Jim Hogue in September of this year, largely my specimens. There were two names det. by JS: Chrysotoxum chinook, and C. integrum. This specimen as well as a couple from the San Gabriel Mountains were identified as integrum.
The latest list, as far as we're aware, is from 4 May, 2014. It includes both derivatum Walker, and integrum Williston as valid names:
CANACOLL Nearctic Syrphidae Checklist.
The list of Flowerflies of Los Angeles County is outdated and will be revised.

here's what Martin had to say: "...there is a Ch. derivatum Walker 1849 and a Ch. derivatum Becker 1921; the latter is a synonym of Ch. caucasicum found in Altai and the Caucasus. Ch. derivatum Walker was described from the Hudson Bay in Canada and Ch. integere Williston 1887 from AZ (and also found in UT, MI, BC, etc.) is a synonym of derivatum Walker. BUT Jeff Skevington is just revising the Chrysotoxum, and there are many new species from CA and I somehow doubt that a species from Canada and AZ are the same, so I have the feeling this synoymy might change in the future. But the mentioning that derivatum Walker has something to do with caucasicum is clearly just wrong, and one might have been confused, because Systema dipterorum gives the valid name without an author, just C. derivatum..."