but not P. californiaria

I took a look around the All Leps website... How would I join that and what would it entail?

See a thread on DNA Barcoding that Mark Dreiling has started in the Forum, and write to Mark for advice about making contact with the folks who run the project at the Univ. of Guelph in Ontario. Basically, once they accept you into the program and send you shipping cartons, pins, etc., you merely "field pin" a specimen (after you have already photographed it) and attach a label to it bearing your log or photo number. When you have accumulated a box of specimens you send them in. They will post DNA results to your data file on their website.

...But I'm not sure about how I feel about dispatching the moths that come to my lights. I'd feel somewhat guilty about removing individuals (particularly females filled with eggs) from the gene pool, especially if they are from rare or endangered species (are there enough data to determine which species are endangered?).

There is just one moth listed as Endangered in California. It is a desert species, Euproserpinus euterpe, the Kern Primrose Sphinx Moth, which is found nowhere near you.