Which species is this white female?

There is no foolproof way to tell all of the sulphur white females apart. From pairings I’ve seen in the field, the Orange white females usually have more dark scaling in the white, broader wing borders (with of course white patches in the border), AND the yellow-orange spot in the center of the dorsal HW is heavy orange rather than yellow (yes, I know, this spot is never exposed while perching – I’ve made these conclusions from net-release specimens handled with forceps). The male-attracted-to-female tactic is not foolproof because these sulphurs are known to occasionally hybridize. In fact, the ones with minimal orange flushes actually may all be hybrids. Many lepidopterists lump the hybrids in with Orange Sulphurs because the Clouded Sulphur is our true native sulphur, whereas the Orange Sulphur invaded the U.S. from Mexico in the 19th century, partly because so many farmers were using alfalfa and red clover, their main hosts, as cattle forage crops.—Dick Smith