Andrena astragali, and a look-alike

This field season I indulged a curiosity about Andrena astragali, an obligate associate of death camas. I looked pretty hard for this species in stands of abundant Toxicoscordion venenosum in the Willamette Valley near Corvallis. My main finding was that T. venenosum was intensively visited by the dronefly Eristalis hirta; A. astragali was not to be found--until I uncovered just one site (Thanks Tom Kaye) with a lively population of A. astragali. Today I was looking at insects collected from Fisher Butte, a site with acres of death camas and swarms of visiting droneflies, but no history (we have 4 years of data) of A. astragali. But we had one:

One of the things I like about astragali is that the ID is straightforward. DiscoverLife narrows to this species pretty quickly with simple characters, which is an unnecessary step if you know the host plant is death camas.

I had a similar-looking Andrena, one of few (in our study sites) with complete tergal hair bands:

But this was collected from Potentilla gracilis, an argument against astragali. In the key, I get to Andrena auricoma. In the description I am told This small western species is very similar to A, astragali but can be separated from the latter by its smaller size, rhomboidal and feebly emarginate labral process, and its shinier terga. Check, check, check. Gratifying, until someone tells me I am wrong.

Posted on September 11, 2022 05:32 AM by cappaert