If we cannot decide on the identity of a species (Noctuidae or other Lepidoptera) by using the wing markings, venations,sizes etc. (namely external characters), then we control preferably male genitalia of the species, to be determined. Because, the male genitalia carries almost always the diagnostic features for the insect species. The female genitalia is usually less important than the males on this point. Of course, for identifying a species, by using the genitalic characters, you had a necessary publication on this subject, at hand.