This is a representative adult of Pontia beckerii, to go with my earlier post about the Becker's White chrysalis.
The plant that it's feeding on is also interesting. I believe this is "diffuse knapweed", Centaurea diffusa, one of the many Centaurea species accidentally introduced from Eurasia in the early 20th century. Diffuse knapweed is another one of those invasive aliens. This one is described by http://el.erdc.usace.army.mil/pmis/plan ... taur3.html as
So, very briefly, this stuff takes over and nothing much eats it. But look on the bright side -- at least it provides a nectar source for these native butterflies, which would otherwise find that pickings get a bit slim this time of year.Growth Characteristics:
Reproduction is exclusively by seed. Being allelopathic, it can dominate disturbed areas almost to the exclusion of other species. It can be distinguished from spotted knapweed which it closely resembles by its spine tipped involucral bracts.
By the late 1980's, 1.3 million ha were infested with diffuse knapweed in western U.S. It rapidly invades overgrazed rangeland and other disturbed sites, and is capable of establishing in undisturbed communities. The foliage contains cnicin and is highly unpalatable resulting in overgrazing of remaining vegetation in rangelands where diffuse knapweed has become established.