As far as I can tell from the photos/context, it appears that the specimen are genuinely wild. At first when there was only a single record, I did not think much of it since there have been occasional one-off records of escapees and such. However, the numbers have steadily climbed in the past month, all from the same general location, up to 5 records now. Anyone in northern California might want to be on the lookout for this species, which may have established a breeding population.
Edit: After a brief look into this species’ life history, I should also add that a breeding population would definitely seem plausible given that the major larval hostplant, bedstraw (Gallium), is a common weed in most of North America. I would also imagine that the mild winters in parts of California would be highly suitable for allowing the adults to overwinter.
I don’t know who the contact would be but it might be worth contacting someone in Cali state agencies to draw their attention to it. I know that they do have a significant inspection presence to reduce invasive species, but no idea even what agency might be best.
Knowing most sphinx species, they usually aren’t picky at all when it comes to exotic vs. native host plants of the correct genus. It looks like the most common Galium species in this part of CA is the European G. aparine, which I presume is widely used in the moths’ native range. The next most common is G. porrigens, a CA native.
Figures! Yeah I know some leps dont care too much at all about food plants (I’ve peered into the world of saturniid rearing before and its really funny how many saturniids, even more tropical taxa, will eat random generic northern hemisphere plants like privet and mulberry and stuff)
If you want relevant people to know about this introduction, there are two main approaches. One, contact the Extension Service in the relevant county. Second, contact the insect or arthropod collection at a major university (e.g UCLA) or the California Academy of Science.
You might have to contact a couple people before you find people who care. And since these eat Galium, which we mainly know as the weed Galium aparine, the extension agent may not be interested – though some would be.
Given the spread of observations (four in a 100km wide area, plus a fifth more than 200km away and on the other side of the Sierras it seems that containment of this species would be extremely difficult, especially since it doesn’t seem to be an agricultural pest. I don’t know much about this species, but the sudden spread of records suggests that there is already an established population that has suddenly started spreading, or someone released a large number of adults in the area.
In Europe the larvae generally feed on Galium sp, but occasionally Madder (Rubia) - very rarely other things. Eggs are sometimes laid on Centranthus - they like this plant as moths - but I can’t find reference to it actually being a larval foodplant. G. aparine (cleavers) is usually too early in the year for them but isn’t unknown, G. verum (Lady’s bedstraw) is more common. I’m not sure if it’s different in California.
I have no doubt they could overwinter in California. They sometimes manage to overwinter in “milder” Europe like Southern England but do so very reliably in Mediterranean Europe; which I believe has a similar climate to much of California.
They are extremely strong fliers and extremely migratory - note how the range in Europe stretches all the way to Scotland and the middle of Scandinavia - when it certainly cannot overwinter that far North. If it is established there I would not be surprised the first few records are so scattered.